Phospho-beta-catenin accumulation in Alzheimer's disease and in aggresomes attributable to proteasome dysfunction

Multi-cohort cerebrospinal fluid proteomics identifies robust molecular signatures across the Alzheimer disease continuum

Changes in β-amyloid (Aβ) and hyperphosphorylated tau (T) in brain and cerebrospinal fluid (CSF) precede Alzheimer's disease (AD) symptoms, making the CSF proteome a potential avenue to understand disease pathophysiology and facilitate reliable diagnostics and therapies. Using the AT framework and a three-stage study design (discovery, replication, and meta-analysis), we identified 2,173 analytes (2,029 unique proteins) dysregulated in AD. Of these, 865 (43%) were previously reported, and 1,164 (57%) are novel. The identified proteins cluster in four different pseudo-trajectories groups spanning the AD continuum and were enriched in pathways including neuronal death, apoptosis, and tau phosphorylation (early stages), microglia dysregulation and endolysosomal dysfunction (mid stages), brain plasticity and longevity (mid stages), and microglia-neuron crosstalk (late stages). Using machine learning, we created and validated highly accurate and replicable (area under the curve [AUC] > 0.90) models that predict AD biomarker positivity and clinical status. These models can also identify people that will convert to AD.

Modulation of the cognitive impairment associated with Alzheimer's disease by valproic acid: possible drug repurposing

Sporadic Alzheimer's disease is a progressive neurodegenerative disorder affecting the central nervous system. Its main two hallmarks are extracellular deposition of aggregated amyloid beta resulting in senile plaques and intracellular hyperphosphorylated tau proteins forming neuro-fibrillary tangles. As those processes are promoted by the glycogen synthase kinase-3 enzyme, GSK3 inhibitors may be of therapeutic value in SAD. GSK3 is also inhibited by the action of insulin on insulin signaling. Insulin receptor desensitization in the brain is hypothesized to cause inhibition of insulin signaling pathway that ultimately causes cognitive deficits seen in SAD. In extant research, induction of cognitive impairment is achieved by intracerebroventricular injection of streptozotocin-a diabetogenic compound that causes desensitization to insulin receptors in the brain leading to the appearance of most of the SAD signs and symptoms. Valproic acid -a histone deacetylase inhibitor and anti-epileptic drug-has been recently studied in the management of SAD as a possible GSK3 inhibitor. Accordingly, the aim of the present study is to explore the role of multiple VPA doses on the downstream effects of the insulin signaling pathway in ICV STZ-injected mice and suggest a possible mechanism of VPA action. ICV STZ-injected mice showed deficiency in short- and long-term memory as well as increased anxiety, as established by open field test, Modified Y-maze, Morris water maze, and elevated plus maze neurobehavioral tests.

Silver nanoparticles induce formation of multi-protein aggregates that contain cadherin but do not colocalize with nanoparticles

Silver nanoparticles (AgNPs) are increasingly incorporated in diverse products to confer antimicrobial properties. They are released into the environment during manufacture, after disposal, and from the products during use. Because AgNPs bioaccumulate in brain, it is important to understand how they interact with neural cell physiology. We found that the focal adhesion (FA)-associated protein cadherin aggregated in a dose-dependent response to AgNP exposure in differentiating cultured B35 neuroblastoma cells. These aggregates tended to colocalize with F-actin inclusions that form in response to AgNP and also contain β-catenin. However, using hyperspectral microscopy, we demonstrate that these multi-protein aggregates did not colocalize with the AgNPs themselves. Furthermore, expression and organization of the FA protein vinculin did not change in cells exposed to AgNP. Our findings suggest that AgNPs activate an intermediate mechanism which leads to formation of aggregates via specific protein-protein interactions. Finally, we detail the changes in hyperspectral profiles of AgNPs during different stages of cell culture and immunocytochemistry processing. AgNPs in citrate-stabilized solution present mostly blue with some rainbow spectra and these are maintained upon mounting in Prolong Gold. Exposure to tissue culture medium results in a uniform green spectral shift that is not further altered by fixation and protein block steps of immunocytochemistry.

Modulating β-catenin homeostasis for cancer therapy

β-Catenin is a well-established driver of many cancers; however, there are challenges in developing agents targeting β-catenin for clinical use. Recent progress has indicated that most of the pathological changes in β-catenin may be commonly caused by loss of protein homeostasis. Modulation of β-catenin homeostasis, especially by hyperactivation of β-catenin, potentially leads to robust antitumor outcomes. Here, we comprehensively dissect the protein homeostasis of β-catenin in terms of time, compartmentalization, supramolecular assemblies, and dynamics, with emphasis on changes in β-catenin homeostasis upon oncogenic mutations. We propose that altered β-catenin homeostasis could be deleterious for β-catenin-dependent cancers and that modulation of β-catenin homeostasis offers a novel avenue for targeting β-catenin for cancer therapy.

The unique neuropathological vulnerability of the human brain to aging

Alzheimer's disease (AD)-related neurofibrillary tangles (NFT), argyrophilic grain disease (AGD), aging-related tau astrogliopathy (ARTAG), limbic predominant TDP-43 proteinopathy (LATE), and amygdala-predominant Lewy body disease (LBD) are proteinopathies that, together with hippocampal sclerosis, progressively appear in the elderly affecting from 50% to 99% of individuals aged 80 years, depending on the disease. These disorders usually converge on the same subject and associate with additive cognitive impairment. Abnormal Tau, TDP-43, and α-synuclein pathologies progress following a pattern consistent with an active cell-to-cell transmission and abnormal protein processing in the host cell. However, cell vulnerability and transmission pathways are specific for each disorder, albeit abnormal proteins may co-localize in particular neurons. All these alterations are unique or highly prevalent in humans. They all affect, at first, the archicortex and paleocortex to extend at later stages to the neocortex and other regions of the telencephalon. These observations show that the phylogenetically oldest areas of the human cerebral cortex and amygdala are not designed to cope with the lifespan of actual humans. New strategies aimed at reducing the functional overload of the human telencephalon, including optimization of dream repair mechanisms and implementation of artificial circuit devices to surrogate specific brain functions, appear promising.

Discovery of bletillain, an unusual benzyl polymer with significant autophagy-inducing effects in A549 lung cancer cells through the Akt/GSK-3β/β-catenin signaling pathway

Lung cancer is one of the most malignant tumors with the highest mortality and morbidity. The tubers of Bletilla striata are known as "an excellent medicine for lung diseases" in traditional Chinese medicine. This study performed a targeted study to explore compounds with anti-lung cancer activity and the molecular mechanisms using A549 cells. Eighteen bibenzyl derivatives, including four new compounds (13, 14, 16, and 18), were isolated from the tubers of B. striata. Analysis of the structure-activity relationship indicated that the cytotoxicity of the bibenzyls against A549 cells increased gradually as the number of the benzyl groups in the structures increased. Bletillain (18), an unusual benzyl polymer, was found to be the most active compound. Further flow cytometric analysis, dual-luciferase assays, real-time PCR assays, and western blot assays revealed that bletillain induced autophagy in A549 cells by regulating the Akt/GSK-3β/β-catenin signaling pathway. Beclin 1, LC3, and p62 are downstream autophagy factors of Akt, and Beclin 1 was the key autophagy factor. These results suggested that bibenzyls of B. striata play important roles in the treatment of lung cancer and provided scientific evidence illustrating why the tubers of B. striata are a suitable medicine for the treatment of lung cancer in traditional Chinese medicine.

Dysregulated Protein Phosphorylation as Main Contributor of Granulovacuolar Degeneration at the First Stages of Neurofibrillary Tangles Pathology

The hippocampus of cases with neurofibrillary tangles (NFT) pathology classified as stages I-II, III-IV, and V-VI without comorbidities, and middle-aged (MA) individuals with no NFT pathology, were examined to learn about the composition of granulovacuolar degeneration (GVD). Our results confirm the presence of CK1-δ, p38-P Thr180/Tyr182, SAPK/JNK-P Thr183/Thr185, GSK-3α/β-P Tyr279/Tyr216, and GSK-3β Ser9 in the cytoplasmic granules in a subset of neurons of the CA1 and CA2 subfields of the hippocampus. Also, we identify the presence of PKA α/β-P Thr197, SRC-P Tyr416, PAK1-P Ser199/Ser204, CAMK2A-P Tyr197, and PKCG-P Thr655 in cytoplasmic granules in cases with NFT pathology, but not in MA cases. Our results also confirm the presence of β-catenin-P Ser45/Thr41, IREα-P Ser274, eIF2α-P Ser51, TDP-43-P Ser403-404 (but absent TDP-43), and ubiquitin in cytoplasmic granules. Other components of the cytoplasmic granules are MAP2-P Thr1620/1623, MAP1B-P Thr1265, ADD1-P Ser726, and ADD1/ADD1-P Ser726/Ser713, in addition to several tau species including 3Rtau, 4Rtau, and tau-P Ser262. The analysis of GVD at progressive stages of NFT pathology reveals the early appearance of phosphorylated kinases and proteins in cytoplasmic granules at stages I-II, before the appearance of pre-tangles and NFTs. Most of these granules are not surrounded by LAMP1-positive membranes. Markers of impaired ubiquitin-protesome system, abnormal reticulum stress response, and altered endocytic and autophagic pathways occur in a subpopulation of neurons containing cytoplasmic granules, and they appear later. These observations suggest early phosphorylation of kinases leading to their activation, and resulting in the abnormal phosphorylation of various substrates, including tau, as a main alteration at the first stages of GVD.

A multitude of signaling pathways associated with Alzheimer's disease and their roles in AD pathogenesis and therapy

The exact molecular mechanisms associated with Alzheimer's disease (AD) pathology continue to represent a mystery. In the past decades, comprehensive data were generated on the involvement of different signaling pathways in the AD pathogenesis. However, the utilization of signaling pathways as potential targets for the development of drugs against AD is rather limited due to the immense complexity of the brain and intricate molecular links between these pathways. Therefore, finding a correlation and cross-talk between these signaling pathways and establishing different therapeutic targets within and between those pathways are needed for better understanding of the biological events responsible for the AD-related neurodegeneration. For example, autophagy is a conservative cellular process that shows link with many other AD-related pathways and is crucial for maintenance of the correct cellular balance by degrading AD-associated pathogenic proteins. Considering the central role of autophagy in AD and its interplay with many other pathways, the finest therapeutic strategy to fight against AD is the use of autophagy as a target. As an essential step in this direction, this comprehensive review represents recent findings on the individual AD-related signaling pathways, describes key features of these pathways and their cross-talk with autophagy, represents current drug development, and introduces some of the multitarget beneficial approaches and strategies for the therapeutic intervention of AD.

Deregulation of signalling in genetic conditions affecting the lysosomal metabolism of cholesterol and galactosyl-sphingolipids

The role of lipids in neuroglial function is gaining momentum in part due to a better understanding of how many lipid species contribute to key cellular signalling pathways at the membrane level. The description of lipid rafts as membrane domains composed by defined classes of lipids such as cholesterol and sphingolipids has greatly helped in our understanding of how cellular signalling can be regulated and compartmentalized in neurons and glial cells. Genetic conditions affecting the metabolism of these lipids greatly impact on how some of these signalling pathways work, providing a context to understand the biological function of the lipid. Expectedly, abnormal metabolism of several lipids such as cholesterol and galactosyl-sphingolipids observed in several metabolic conditions involving lysosomal dysfunction are often accompanied by neuronal and myelin dysfunction. This review will discuss the role of lysosomal biology in the context of deficiencies in the metabolism of cholesterol and galactosyl-sphingolipids and their impact on neural function in three genetic disorders: Niemann-Pick type C, Metachromatic leukodystrophy and Krabbe's disease.

Wnt Signaling Pathway Dysregulation in the Aging Brain: Lessons From the Octodon degus

Wnt signaling constitutes a fundamental cellular and molecular pathway, necessary from proper embryogenesis to function-maintenance of fully developed complex organisms. In this regard, Wnt pathway plays a crucial role in both the development of the central nervous system and in maintaining the structure and function of the neuronal circuits, and it has been suggested that its dysregulation is critical in the onset of several pathologies including cancer and neurodegenerative disorders, such as Alzheimer's disease (AD). Due to its relevance in the maintenance of the neuronal activity and its involvement in the outbreak of devastating diseases, we explored the age-related changes in the expression of Wnt key components in the cortex and hippocampus of 7 to 72-months-old Octodon degus (O. degus), a Chilean long-living endemic rodent that has been proposed and used as a natural model for AD. We found a down-regulation in the expression of different Wnt ligands (Wnt3a, Wnt7a, and Wnt5a), as well as in the Wnt co-receptor LRP6. We also observed an increase in the activity of GSK-3β related to the down-regulation of Wnt activity, a fact that was confirmed by a decreased expression of Wnt target genes. Relevantly, an important increase was found in secreted endogenous Wnt inhibitors, including the secreted-frizzled-related protein 1 and 2 (SFRP-1 and SFRP-2) and Dickkopf-1 (Dkk-1), all them antagonists at the cell surface. Furthermore, treatment with Andrographolide, a labdane diterpene obtained from Andrographis paniculata, prevents Wnt signaling loss in aging degus. Taken together, these results suggest that during the aging process Wnt signaling activity decreases in the brain of O. degus.

β-catenin aggregation in models of ALS motor neurons: GSK3β inhibition effect and neuronal differentiation

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by motor neuron death. A 20% of familial ALS cases are associated with mutations in the gene coding for superoxide dismutase 1 (SOD1). The accumulation of abnormal aggregates of different proteins is a common feature in motor neurons of patients and transgenic ALS mice models, which are thought to contribute to disease pathogenesis. Developmental morphogens, such as the Wnt family, regulate numerous features of neuronal physiology in the adult brain and have been implicated in neurodegeneration. β-catenin is a central mediator of both, Wnt signaling activity and cell-cell interactions. We previously reported that the expression of mutant SOD1 in the NSC34 motor neuron cell line decreases basal Wnt pathway activity, which correlates with cytosolic β-catenin accumulation and impaired neuronal differentiation. In this work, we aimed a deeper characterization of β-catenin distribution in models of ALS motor neurons. We observed extensive accumulation of β-catenin supramolecular structures in motor neuron somas of pre-symptomatic mutant SOD1 mice. In cell-cell appositional zones of NSC34 cells expressing mutant SOD1, β-catenin displays a reduced co-distribution with E-cadherin accompanied by an increased association with the gap junction protein Connexin-43; these findings correlate with impaired intercellular adhesion and exacerbated cell coupling. Remarkably, pharmacological inhibition of the glycogen synthase kinase-3β (GSK3β) in both NSC34 cell lines reverted both, β-catenin aggregation and the adverse effects of mutant SOD1 expression on neuronal differentiation. Our findings suggest that early defects in β-catenin distribution could be an underlying factor affecting the onset of neurodegeneration in familial ALS.

Single-cell transcriptomics unveils gene regulatory network plasticity

BACKGROUND

Single-cell RNA sequencing (scRNA-seq) plays a pivotal role in our understanding of cellular heterogeneity. Current analytical workflows are driven by categorizing principles that consider cells as individual entities and classify them into complex taxonomies.

RESULTS

We devise a conceptually different computational framework based on a holistic view, where single-cell datasets are used to infer global, large-scale regulatory networks. We develop correlation metrics that are specifically tailored to single-cell data, and then generate, validate, and interpret single-cell-derived regulatory networks from organs and perturbed systems, such as diabetes and Alzheimer's disease. Using tools from graph theory, we compute an unbiased quantification of a gene's biological relevance and accurately pinpoint key players in organ function and drivers of diseases.

CONCLUSIONS

Our approach detects multiple latent regulatory changes that are invisible to single-cell workflows based on clustering or differential expression analysis, significantly broadening the biological insights that can be obtained with this leading technology.

Alteration of the Wnt/GSK3β/β‑catenin signalling pathway by rapamycin ameliorates pathology in an Alzheimer's disease model

The abnormal activation of glycogen synthase kinase 3β (GSK3β) is one of the mechanisms involved in the pathogenesis of Alzheimer's disease (AD), which results in amyloid β‑peptide (Aβ) plaque overproduction, Tau hyperphosphorylation and neuronal loss. A number of studies have reported that the activation of the mammalian target of rapamycin (mTOR) contributes to the generation and deposition of Aβ, as well as to the formation of neurofibrillary tangles (NFTs) by inhibiting autophagy. GSK3β is also involved in the mTOR signalling pathway. However, whether the inhibition of the activation of mTOR via the regulation of the function of GSK3β affects the pathology of AD remains unclear. In this study, we intraperitoneally injected amyloid precursor protein (APP)/presenilin‑1 (PS1) transgenic mice with rapamycin, a known activator of autophagy that inhibits mTOR. Our results revealed that rapamycin treatment decreased senile plaque deposition by reducing APP generation, and downregulating β‑ and γ‑secretase activity. Rapamycin also increased Aβ clearance by promoting autophagy and reduced Tau hyperphosphorylation by upregulating the levels of insulin‑degrading enzyme. Additionally, rapamycin markedly promoted the proliferation of differentiated SH‑SY5Y cells stably transfected with the APPswe gene and prevented neuronal loss in the brains of mice in a model of AD. Moreover, rapamycin induced autophagy and promoted autolysosome degradation. In this study, we provide evidence that rapamycin inhibits GSK3β activation and elevates β‑catenin expression by improving the Wnt3a expression levels, which facilitates the amelioration of AD pathology. On the whole, our findings indicate that rapamycin inhibits the activation of mTOR and alters the Wnt/GSK3β/β‑catenin signalling pathway; thus, it may serve as a therapeutic target in the treatment of AD.

Single-Base Resolution Mapping of 5-Hydroxymethylcytosine Modifications in Hippocampus of Alzheimer's Disease Subjects

Epigenetic modifications to cytosine have been shown to regulate transcription in cancer, embryonic development, and recently neurodegeneration. While cytosine methylation studies are now common in neurodegenerative research, hydroxymethylation studies are rare, particularly genome-wide mapping studies. As an initial study to analyze 5-hydroxymethylcytosine (5-hmC) in the Alzheimer's disease (AD) genome, reduced representation hydroxymethylation profiling (RRHP) was used to analyze more than 2 million sites of possible modification in hippocampal DNA of sporadic AD and normal control subjects. Genes with differentially hydroxymethylated regions were filtered based on previously published microarray data for altered gene expression in hippocampal DNA of AD subjects. Our data show significant pathways for altered levels of 5-hmC in the hippocampus of AD subjects compared to age-matched normal controls involved in signaling, energy metabolism, cell function, gene expression, protein degradation, and cell structure and stabilization. Overall, our data suggest a possible role for the dysregulation of epigenetic modifications to cytosine in late stage AD.

Granulovacuolar degeneration: a neurodegenerative change that accompanies tau pathology

Granule-containing vacuoles in the cytoplasm of hippocampal neurons are a neuropathological feature of Alzheimer's disease. Granulovacuolar degeneration (GVD) is not disease-specific and can be observed in other neurodegenerative disorders and even in the brains of non-demented elderly people. However, several studies have reported much higher numbers of neurons undergoing GVD in the hippocampus of Alzheimer's disease cases. Recently, a neuropathological staging system for GVD has facilitated neuropathological assessment. Data obtained by electron microscopy and immunolabeling suggest that GVD inclusions are a special form of autophagic vacuole. GVD frequently occurs together with pathological changes of the microtubule-associated protein tau, but to date, the relationship between the two lesions remains elusive. Originally identified in hematoxylin- and silver-stained sections, immunolabeling has shown that the granules are composed of a variety of proteins, including those related to tau pathology, autophagy, diverse signal transduction pathways, cell stress and apoptosis. Several of these proteins serve as markers of GVD. Most researchers and authors have interpreted the sequestration of proteins into GVD inclusions as either a cellular defense mechanism or one that leads to the impairment of important cellular functions. This review provides a detailed overview of the various aspects of GVD and focuses on the relationship between tau pathology and GVD.

It Is All about (U)biquitin: Role of Altered Ubiquitin-Proteasome System and UCHL1 in Alzheimer Disease

Free radical-mediated damage to macromolecules and the resulting oxidative modification of different cellular components are a common feature of aging, and this process becomes much more pronounced in age-associated pathologies, including Alzheimer disease (AD). In particular, proteins are particularly sensitive to oxidative stress-induced damage and these irreversible modifications lead to the alteration of protein structure and function. In order to maintain cell homeostasis, these oxidized/damaged proteins have to be removed in order to prevent their toxic accumulation. It is generally accepted that the age-related accumulation of “aberrant” proteins results from both the increased occurrence of damage and the decreased efficiency of degradative systems. One of the most important cellular proteolytic systems responsible for the removal of oxidized proteins in the cytosol and in the nucleus is the proteasomal system. Several studies have demonstrated the impairment of the proteasome in AD thus suggesting a direct link between accumulation of oxidized/misfolded proteins and reduction of this clearance system. In this review we discuss the impairment of the proteasome system as a consequence of oxidative stress and how this contributes to AD neuropathology. Further, we focus the attention on the oxidative modifications of a key component of the ubiquitin-proteasome pathway, UCHL1, which lead to the impairment of its activity.

Remarkable impairment of Wnt/β-catenin signaling in the brains of the mice infected with scrapie agents

Prion diseases are a group of neurodegenerative diseases characterized by neuronal loss and spongiform degeneration, astrogliosis and aggregation of scrapie prion protein (PrP^Sc ) in the central nervous system (CNS). The Wnt signaling pathway is a highly evolutionarily conserved pathway in eukaryotes that regulates cell proliferation, differentiation and survival. Impairment of Wnt/β-catenin signaling has been reported in the CNS of various neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. To investigate the functional state of Wnt/β-catenin signaling in the CNS tissues during the progression of prion disease, the components of Wnt/β-catenin signaling in the brains of the scrapie agents 139A- and ME7-infected mice were evaluated. Compared with the normal controls, the brain levels of phosphor-β-catenin (Ser^33,37 and Thr⁴¹ ) in 139A- and ME7-infected mice were significantly increased, while those of cyclin D1, which is one of the target genes of Wnt signaling, were decreased. The levels of phosphor-glycogen synthase kinase-3β (GSK-3β) Ser⁹ were markedly reduced, representing an enhanced GSK-3β activity in scrapie-infected mice. Both western blot and immunohistochemical assays revealed a remarkable increase of Dickkopf-1, the antagonist of Wnt/β-catenin signaling, in the brains of scrapie-infected anim-als, which co-localized well with the remaining neurons in the immunofluorescent tests. We also observed slightly decreased Wnt-3 and unchanged disheveled-3 (Dvl-3) in the brains of the infected mice. Our data, here, strongly indicate an impairment of Wnt/β-catenin pathway in the brains of prion disease, which shows a time-dependent progression along with the incubation period. Schematic for the impairment of canonical Wnt signaling during prion infection. The left and right parts represent the normal and prion-infected situations, respectively. Prion infection or PrP^Sc accumulation triggers the over-expression of Dickkopf WNT signaling pathway inhibitor 1 (DKK-1) and the enhancement of glycogen synthase kinase 3β (GSK-3β) activity, which subsequently promotes the phosphorylation and degradation of β-catenin. As a result, the impairment of β-catenin signaling leads to the down-regulation of Wnt target genes.

Antioxidative effects of ethyl 2-(3-(benzo[d]thiazol-2-yl)ureido)acetate against amyloid β-induced oxidative cell death via NF-κB, GSK-3β and β-catenin signaling pathways in cultured cortical neurons

We have previously shown that 2-(3-(benzo[d]thiazol-2-yl)ureido)acetate (KHG21834) attenuates amyloid beta(Aβ)25-35-induced apoptotic death and shows anti-inflammatory activity against Aβ25-35-induced microglial activation. However, antioxidative effects of KHG21834 against Aβ-induced oxidative stress have not yet been reported. In the present study, we investigated the antioxidative function of KHG21834 in primary cultured cortical neurons, to expand the potential therapeutic efficacy of KHG21834. Pretreatment with KHG21834 protected against Aβ-induced neuronal cell death and mitochondrial damage, and significantly restored GSH levels and the activities of catalase, superoxide dismutase, and glutathione peroxidase, and also suppressed the production of reactive oxygen species and protein oxidation. These results imply that KHG21834 may play a role in cellular defense mechanisms against Aβ-induced oxidative stress in cultured cortical neurons. Furthermore, KHG21834 significantly attenuated the effects of Aβ treatment on levels of NF-κB, β-catenin, and GSK-3β proteins in cortical neurons. Taken together, our results suggest that the antioxidant effects of KHG21834 may result at least in part from its ability to regulate the NF-κB, β-catenin, and GSK-3β signaling pathways. To our knowledge, this is the first report showing that KHG21834 significantly attenuates Aβ25-35-induced oxidative stress in primary cortical neurons, and provides novel insights into KHG21834 as a possible therapeutic agent for the treatment of Aβ-mediated neurotoxicity involving oxidative stress.

Wnt signaling in the nervous system and in Alzheimer's disease

Wnts comprise a large family of proteins that have shown to be part of a signaling cascade that regulates several aspects of development including organogenesis, midbrain development as well as stem cell proliferation. Wnt signaling pathway plays different roles in the development of neuronal circuits and also in the adult brain, where it regulates synaptic transmission and plasticity. It has been also implicated in various diseases including cancer and neurodegenerative diseases, reflecting its relevance in fundamental biological processes. This review summarizes the progress about Wnts function in mature nervous system with a focus on Alzheimer's disease (AD). We discuss the prospects of modulating canonical and non-canonical Wnt signaling as a strategy for neuroprotection. This will include the potential of Wnts to: (i) act as potent regulators of hippocampal synapses and impact in learning and memory; (ii) regulate adult neurogenesis; and finally (iii) control AD pathogenesis.

The crucial role of Atg5 in cortical neurogenesis during early brain development

Autophagy plays an important role in the central nervous system. However, it is unknown how autophagy regulates cortical neurogenesis during early brain development. Here, we report that autophagy-related gene 5 (Atg5) expression increased with cortical development and differentiation. The suppression of Atg5 expression by knockdown led to inhibited differentiation and increased proliferation of cortical neural progenitor cells (NPCs). Additionally, Atg5 suppression impaired cortical neuronal cell morphology. We lastly observed that Atg5 was involved in the regulation of the β-Catenin signaling pathway. The β-Catenin phosphorylation level decreased when Atg5 was blocked. Atg5 cooperated with β-Catenin to modulate cortical NPCs differentiation and proliferation. Our results revealed that Atg5 has a crucial role in cortical neurogenesis during early embryonic brain development, which may contribute to the understanding of neurodevelopmental disorders caused by autophagy dysregulation.

Pen-2 is essential for γ-secretase complex stability and trafficking but partially dispensable for endoproteolysis

The 19-transmembrane γ-secretase complex generates the amyloid β-peptide of Alzheimer’s disease by intramembrane proteolysis of the β-amyloid precursor protein. This complex is comprised of presenilin, Aph1, nicastrin, and Pen-2. The exact function and mechanism of the highly conserved Pen-2 subunit remain poorly understood. Using systematic mutagenesis, we confirm and extend our understanding of which key regions and specific residues play roles in various aspects of γ-secretase function, including maturation, localization, and activity, but not processivity. In general, mutations (1) within the first half of transmembrane domain (TMD) 1 of Pen-2 decreased PS1 endoproteolysis and γ-secretase proteolytic activity, (2) within the second half of TMD1 increased proteolytic activity, (3) within the cytosolic loop region decreased proteolytic activity, (4) within TMD2 decreased PS1 endoproteolysis, (5) within the first half of TMD2 decreased proteolytic activity, and (6) within C-terminal residues decreased proteolytic activity. Specific mutational effects included N33A in TMD1 causing an increase in γ-secretase complexes at the cell surface and a modest decrease in stability and the previously unreported I53A mutation in the loop region reducing stability 10-fold and proteolytic activity by half. In addition, we confirm that minor PS1 endoproteolysis can occur in the complete absence of Pen-2. Together, these data suggest that rather than solely being a catalyst for γ-secretase endoproteolysis, Pen-2 may also stabilize the complex prior to PS1 endoproteolysis, allowing time for full assembly and proper trafficking.

Chronic hypoxia induces the activation of the Wnt/β-catenin signaling pathway and stimulates hippocampal neurogenesis in wild-type and APPswe-PS1ΔE9 transgenic mice in vivo

Hypoxia modulates proliferation and differentiation of cultured embryonic and adult stem cells, an effect that includes β-catenin, a key component of the canonical Wnt signaling pathway. Here we studied the effect of mild hypoxia on the activity of the Wnt/β-catenin signaling pathway in the hippocampus of adult mice in vivo. The hypoxia-inducible transcription factor-1α (HIF-1α) was analyzed as a molecular control of the physiological hypoxic response. Exposure to chronic hypoxia (10% oxygen for 6–72 h) stimulated the activation of the Wnt/β-catenin signaling pathway. Because the Wnt/β-catenin pathway is a positive modulator of adult neurogenesis, we evaluated whether chronic hypoxia was able to stimulate neurogenesis in the subgranular zone (SGZ) of the hippocampal dentate gyrus. Results indicate that hypoxia increased cell proliferation and neurogenesis in adult wild-type mice as determined by Ki67 staining, Bromodeoxyuridine (BrdU) incorporation and double labeling with doublecortin (DCX). Chronic hypoxia also induced neurogenesis in a double transgenic APPswe-PS1ΔE9 mouse model of Alzheimer’s disease (AD), which shows decreased levels of neurogenesis in the SGZ. Our results show for the first time that exposure to hypoxia in vivo can induce the activation of the Wnt/β-catenin signaling cascade in the hippocampus, suggesting that mild hypoxia may have a therapeutic value in neurodegenerative disorders associated with altered Wnt signaling in the brain and also in pathological conditions in which hippocampal neurogenesis is impaired.

HIF-1α Provokes Delayed Neutrophil Apoptosis by Decreasing 24P3 Expression and Intracellular Iron Content

Neutrophil apoptosis is delayed in medical conditions associated to anoxia or hypoxia, prolonging tissue destruction and fostering the inflammation. Hypoxia Inducible Factor-1α (HIF-1α), is a main regulator of delayed neutrophil apoptosis but the mechanism of action is poorly characterized. Neutrophil gelatinase-associated lipocalin (24p3) participates actively in iron metabolism and the regulation of iron-responsive genes. Recently, a connection has been described between HIF-1α and 24p3. The purpose of the present study was to determine whether constitutive apoptosis in neutrophils requires 24p3 and whether HIF-1α represses 24p3 affecting cell death iron intracellular levels. To this end we used in vivo ischemic models and anoxic approaches based on the reactivation of the delayed apoptosis. We found that the stabilization of HIF-α during anoxic periods provoked a delay in neutrophil apoptosis through decrease of 24p3 expression and intracellular iron content. The ischemia drastically inhibited the synthesis of 24p3 in circulating neutrophils, increasing the tissue damage. Reactivation of neutrophil apoptosis with opsonized E.coli induced increases in intracellular levels of iron and 24p3. In conclusion, contrary to other cell types, constitutive apoptosis in neutrophils requires 24p3. During hypoxia or ischemia, HIF-1α stabilization represses 24p3 expression, consequently iron levels are depleted and neutrophil apoptosis is delayed.

Characterization of Wnt/β-catenin and BMP/Smad signaling pathways in an in vitro model of amyotrophic lateral sclerosis

Different pathways activated by morphogens of the early embryonic development, such as the Wnt and the Bone Morphogenetic Protein (BMP) ligands, are involved in diverse physiological and pathological conditions of the nervous system, including neurodegeneration. In this work, we have analyzed the endogenous activity of the canonical Wnt/β-catenin and BMP/Smad-dependent pathways in an in vitro model of amyotrophic lateral sclerosis (ALS), given by motor neuron-like NSC34 cells stably expressing wild-type or G93A mutated forms of human Cu/Zn superoxide dismutase-1 (SOD1). As ALS-derived motor neurons, NSC34 cells expressing mutated hSOD1 show a decreased proliferation rate, are more susceptible to oxidation-induced cell death and display Golgi fragmentation. In addition, they display an impaired ability to induce the expression of the motor neuronal marker Hb9 and, consistently, to morphologically differentiate into a motor neuronal phenotype. Regarding signaling, our data show that the transcriptional activity associated to the Wnt/β-catenin pathway is decreased, a finding possibly associated to the cytosolic aggregation of β-catenin. In turn, the BMP-dependent phosphorylation of Smad1 and the transcriptional activation of the BMP/Smad pathway is increased in the pathologic model. Together, these findings suggest that Wnt/β-catenin and the BMP-dependent pathways could play relevant roles in the neurodegeneration of motor neurons in the context of ALS.

WNT signaling in neuronal maturation and synaptogenesis

The Wnt signaling pathway plays a role in the development of the central nervous system and growing evidence indicates that Wnts also regulates the structure and function of the adult nervous system. Wnt components are key regulators of a variety of developmental processes, including embryonic patterning, cell specification, and cell polarity. In the nervous system, Wnt signaling also regulates the formation and function of neuronal circuits by controlling neuronal differentiation, axon outgrowth and guidance, dendrite development, synaptic function, and neuronal plasticity. Wnt factors can signal through three very well characterized cascades: canonical or β-catenin pathway, planar cell polarity pathway and calcium pathway that control different processes. However, divergent downstream cascades have been identified to control neuronal morphogenesis. In the nervous system, the expression of Wnt proteins is a highly controlled process. In addition, deregulation of Wnt signaling has been associated with neurodegenerative diseases. Here, we will review different aspects of neuronal and dendrite maturation, including spinogenesis and synaptogenesis. Finally, the role of Wnt pathway components on Alzheimer’s disease will be revised.

Interaction between misfolded PrP and the ubiquitin-proteasome system in prion-mediated neurodegeneration

Prion diseases are associated with the conformational conversion of cellular prion protein (PrP(C)) to pathological β-sheet isoforms (PrP(Sc)), which is the infectious agent beyond comprehension. Increasing evidence indicated that an unknown toxic gain of function of PrP(sc) underlies neuronal death. Conversely, strong evidence indicated that cellular prion protein might be directly cytotoxic by mediating neurotoxic signaling of β-sheet-rich conformers independent of prion replication. Furthermore, the common properties of β-sheet-rich isoform such as PrP(Sc) and β amyloid protein become the lynchpin that interprets the general pathological mechanism of protein misfolding diseases. Dysfunction of the ubiquitin-proteasome system (UPS) has been implicated in various protein misfolding diseases. However, the mechanisms of this impairment remain unknown in many cases. In prion disease, prion-infected mouse brains have increased levels of ubiquitin conjugates, which correlate with decreased proteasome function. Both PrP(C) and PrP(Sc) accumulate in cells after proteasome inhibition, which leads to increased cell death. A direct interaction between 20S core particle and PrP isoforms was demonstrated. Here we review the ability of misfolded PrP and UPS to affect each other, which might contribute to the pathological features of prion-mediated neurodegeneration.

Wnt signaling: role in Alzheimer disease and schizophrenia

Wnt signaling function starts during the development of the nervous system and is crucial for synaptic plasticity in the adult brain. Clearly Wnt effects in synaptic and plastic processes are relevant, however the implication of this pathway in the prevention of neurodegenerative diseases that produce synaptic impairment, is even more interesting. Several years ago our laboratory found a relationship between the loss of Wnt signaling and the neurotoxicity of the amyloid-β-peptide (Aβ), one of the main players in Alzheimer's disease (AD). Moreover, the activation of the Wnt signaling cascade prevents Aβ-dependent cytotoxic effects. In fact, disrupted Wnt signaling may be a direct link between Aβ-toxicity and tau hyperphosphorylation, ultimately leading to impaired synaptic plasticity and/or neuronal degeneration, indicating that a single pathway can account for both neuro-pathological lesions and altered synaptic function. These observations, suggest that a sustained loss of Wnt signaling function may be a key relevant factor in the pathology of AD. On the other hand, Schizophrenia remains one of the most debilitating and intractable illness in psychiatry. Since Wnt signaling is important in organizing the developing brain, it is reasonable to propose that defects in Wnt signaling could contribute to Schizophrenia, particularly since the neuro-developmental hypothesis of the disease implies subtle dys-regulation of brain development, including some core components of the Wnt signaling pathways such as GSK-3β or Disrupted in Schizophrenia-1 (DISC-1). This review focuses on the relationship between Wnt signaling and its potential relevance for the treatment of neurodegenerative and neuropsychiatric diseases including AD and Schizophrenia.

Human cytomegalovirus infection dysregulates the canonical Wnt/β-catenin signaling pathway

Human Cytomegalovirus (HCMV) is a ubiquitous herpesvirus that currently infects a large percentage of the world population. Although usually asymptomatic in healthy individuals, HCMV infection during pregnancy may cause spontaneous abortions, premature delivery, or permanent neurological disabilities in infants infected in utero. During infection, the virus exerts control over a multitude of host signaling pathways. Wnt/β-catenin signaling, an essential pathway involved in cell cycle control, differentiation, embryonic development, placentation and metastasis, is frequently dysregulated by viruses. How HCMV infection affects this critical pathway is not currently known. In this study, we demonstrate that HCMV dysregulates Wnt/β-catenin signaling in dermal fibroblasts and human placental extravillous trophoblasts. Infection inhibits Wnt-induced transcriptional activity of β-catenin and expression of β-catenin target genes in these cells. HCMV infection leads to β-catenin protein accumulation in a discrete juxtanuclear region. Levels of β-catenin in membrane-associated and cytosolic pools, as well as nuclear β-catenin, are reduced after infection; while transcription of the β-catenin gene is unchanged, suggesting enhanced degradation. Given the critical role of Wnt/β-catenin signaling in cellular processes, these findings represent a novel and important mechanism whereby HCMV disrupts normal cellular function.

A large percentage of the world population is infected with HCMV. As a leading viral cause of birth defects in the developed world, HCMV represents a significant public health burden. For the first time, we report that HCMV infection dysregulates the canonical Wnt/β-catenin signaling pathway which is essential in regulating a diverse range of biological functions. We demonstrate that HCMV infection leads to sequestration and degradation of β-catenin protein, the effector transcription factor in the pathway, thus preventing its downstream signaling activities. Since this pathway is essential in regulating mammalian development and homeostasis, the finding that HCMV impairs this pathway becomes globally important for understanding viral pathogenesis, particularly that related to HCMV disease.

WISP1 (CCN4) autoregulates its expression and nuclear trafficking of β-catenin during oxidant stress with limited effects upon neuronal autophagy

Wnt1 inducible signaling pathway protein 1 (WISP1/CCN4) is a CCN family member more broadly identified with development and tumorigenesis. However, recent studies have shed new light and enthusiasm on WISP1 as a novel target directed against toxic cell degeneration. Here we show WISP1 prevents apoptotic degeneration in primary neurons during oxidant stress through the activation of protein kinase B (Akt1), the post-translational maintenance of β-catenin integrity that is consistent with inhibition of glycogen synthase kinase-3β (GSK-3β), and the subcellular trafficking of β- catenin to foster its translocation to the nucleus. Interestingly, WISP1 autoregulates its expression through the promotion of β-catenin activity and may employ β-catenin to have a limited control over autophagy, but neuronal injury during oxidant stress as a result of autophagy appears portioned to a small population of neurons without significant impact upon overall cell survival. New strategies that target WISP1, its autoregulation, and the pathways responsible for neuronal cell injury may bring forth new insight for the treatment of neurodegenerative disorders.

Amyloid precursor protein accumulates in aggresomes in response to proteasome inhibitor

Aggresomes are cytoplasmic inclusions which are localized at the microtubule organizing center (MTOC) as a result of induced proteasome inhibition, stress or over-expression of certain proteins. Aggresomes are linked to the pathogenesis of many neurodegenerative diseases. Here we studied whether amyloid precursor protein (APP), a type-I transmembrane glycoprotein, is localized in aggresomes after exposure to stress condition. Using confocal microscopy we found that APP is located in aggresomes and co-localized with vimentin, γ-tubulin, 20S and ubiquitin at the MTOC in response to proteasome dysfunction. An interaction between vimentin and APP was found after proteasome inhibition suggesting that APP is an additional protein constituent of aggresomes. Suppression of the proteasome system in APP-HEK293 cells overexpressing APP or transfected with APP Swedish mutation caused an accumulation of stable, detergent-insoluble forms of APP containing poly-ubiquitinated proteins. In addition, brain homogenates from transgenic mice expressing human APP with the Arctic mutation demonstrated an interaction between APP and the aggresomal-marker vimentin. These data suggest that malfunctioning of the proteasome system caused by mutation or overexpression of pathological or non-pathological proteins may lead to the accumulation of stable aggresomes, perhaps contributing to the neurodegeneration.

Granulovacuolar degenerations appear in relation to hippocampal phosphorylated tau accumulation in various neurodegenerative disorders

Background

Granulovacuolar degeneration (GVD) is one of the pathological hallmarks of Alzheimer's disease (AD), and it is defined as electron-dense granules within double membrane-bound cytoplasmic vacuoles. Several lines of evidence have suggested that GVDs appear within hippocampal pyramidal neurons in AD when phosphorylated tau begins to aggregate into early-stage neurofibrillary tangles. The aim of this study is to investigate the association of GVDs with phosphorylated tau pathology to determine whether GVDs and phosphorylated tau coexist among different non-AD neurodegenerative disorders.

Methods

An autopsied series of 28 patients with a variety of neurodegenerative disorders and 9 control patients were evaluated. Standard histological stains along with immunohistochemistry using protein markers for GVD and confocal microscopy were utilized.

Results

The number of neurons with GVDs significantly increased with the level of phosphorylated tau accumulation in the hippocampal regions in non-AD neurodegenerative disorders. At the cellular level, diffuse staining for phosphorylated tau was detected in neurons with GVDs.

Conclusions

Our data suggest that GVDs appear in relation to hippocampal phosphorylated tau accumulation in various neurodegenerative disorders, while the presence of phosphorylated tau in GVD-harbouring neurons in non-AD neurodegenerative disorders was indistinguishable from age-related accumulation of phosphorylated tau. Although GVDs in non-AD neurodegenerative disorders have not been studied thoroughly, our results suggest that they are not incidental findings, but rather they appear in relation to phosphorylated tau accumulation, further highlighting the role of GVD in the process of phosphorylated tau accumulation.

Microarray analysis of the astrocyte transcriptome in the aging brain: relationship to Alzheimer's pathology and APOE genotype

Astrocytes contribute to a variety of functions in the brain, including homeostasis, synapse formation, plasticity, and metabolism. Astrocyte dysfunction may disrupt their normal role, including neuronal support, thereby contributing to neurodegenerative pathologies, including Alzheimer's disease (AD). To understand the role of astrocytes in the pathogenesis of age-related disorders, we isolated astrocytes by laser capture microdissection, using glial fibrillary acidic protein (GFAP) as a marker, and characterized the astrocyte transcriptome at different Braak neurofibrillary tangle stages in postmortem temporal cortex samples derived from the Medical Research Council Cognitive Function and Ageing Study (MRC CFAS) cohort, using microarray analysis. The largest number of significant, differentially expressed genes were identified when the expression profile of astrocytes from isocortical stages of neurofibrillary tangle pathology (Braak stages V-VI) were compared with entorhinal stages (Braak stages I-II). Dysregulation of genes associated with the actin cytoskeleton, proliferation, apoptosis, and ubiquitin-mediated proteolysis occurred at low Braak stages, while altered regulation of intracellular signaling pathways, including insulin, phosphatidylinositol 3-kinase (PI3K)/Akt, and mitogen-activated protein kinase (MAPK) pathways were primarily associated with high levels of Alzheimer-type pathology, and occurred at lower Braak stages in individuals with the APOEε4 allele. Our findings implicate astrocyte dysfunction in the pathogenesis of neurodegenerative pathology in the aging brain, and provide a basis for future candidate studies based on specific pathways.

The role of the ubiquitin proteasome system in Alzheimer's disease

Today, Alzheimer's disease (AD) is one of the most important age-related neurodegenerative diseases, but its etiology remains still unknown. Since the discovery that the hallmark structures of this disease i.e. the formation of amyloid fibers could be the product of ubiquitin-mediated protein degradation defects, it has become clear that the ubiquitin–proteasome system (UPS), usually essential for protein repair, turnover and degradation, is perturbed in this disease. Different aspects of normal and pathological aging are discussed with respect to protein repair and degradation via the UPS, as well as consequences of a deficit in the UPS in AD. Selective protein oxidation may cause protein damage, or protein mutations may induce a dysfunction of the proteasome. Such events eventually lead to activation of cell death pathways and to an aberrant aggregation or incorporation of ubiquitinated proteins into hallmark structures. Aggresome formation is also observed in other neurodegenerative diseases, suggesting that an activation of similar mechanisms must occur in neurodegeneration as a basic phenomenon. It is essential to discuss therapeutic ways to investigate the UPS dysfunction in the human brain and to identify specific targets to hold or stop cell decay.

Curcumin activates Wnt/β-catenin signaling pathway through inhibiting the activity of GSK-3β in APPswe transfected SY5Y cells

Wnt/β-catenin signaling pathway plays an important role in the genesis and development of Alzheimer's disease. The study aims to investigate the effect of Curcumin on the expression of GSK-3β, β-catenin and CyclinD1 in vitro, which are tightly correlated with Wnt/β-catenin signaling pathway, and also to explore the mechanisms, which will provide a novel therapeutic intervention for treatment of Alzheimer's disease. Plasmid APPswe and BACE1-mychis were transiently co-transfected into SHSY5Y cells by Liposfectamin™2000. The cells were treated with Curcumin at 0, 1.25, 5.0, 20.0 μmol/L for 24 h, or with Curcumin at 5.0 μmol/L for 0, and 12, 24 and 48 h for time course assay. Cell lysates were collected for RT-PCR, Western blot assay and immunofluorescent staining were carried out for detecting the effect of Curcumin on the expression of GSK-3β, β-catenin and CyclinD1. RT-PCR and Western blot results showed that the expression of GSK-3β mRNA and protein significantly decreased in the transfected cells treated with Curcumin, and that the changes were in a dose and time-dependent manner (P<0.05); however, the protein expression of GSK-3β-Ser9 was increased (P<0.05). Meanwhile, the expressions of β-catenin and transcriptional factors CyclinD1 mRNA and protein increased and the changes were also in a dose and time-dependent manner (P<0.05). Immunofluorescent staining results not only confirmed the above changes, but also showed that β-catenin had translocated into the nucleus gradually with the increased dosage of Curcumin. Therefore, GSK-3β is a potential target for treatment of AD. Curcumin could activate the Wnt/β-catenin signaling pathway through inhibiting the expression of GSK-3β and inducing the expression of β-catenin and CyclinD1, which will provide a new theory for treatment of neurodegenerative diseases by Curcumin.

Identification of novel candidate genes for Alzheimer's disease by autozygosity mapping using genome wide SNP data

Alzheimer's disease (AD) is highly prevalent in Wadi Ara despite the low frequency of apolipoprotein E ε4 in this genetically isolated Arab community in northern Israel. We hypothesized that the reduced genetic variability in combination with increased homozygosity would facilitate identification of genetic variants that contribute to the high rate of AD in this community. AD cases (n = 124) and controls (n = 142) from Wadi Ara were genotyped for a genome-wide set of more than 300,000 single nucleotides polymorphisms (SNPs) which were used to calculate measures of population stratification and inbreeding, and to identify regions of autozygosity. Although a high degree of relatedness was evident in both AD cases and controls, controls were significantly more related and contained more autozygous regions than AD cases (p = 0.004). Eight autozygous regions on seven different chromosomes were more frequent in controls than the AD cases, and 116 SNPs in these regions, primarily on chromosomes 2, 6, and 9, were nominally associated with AD. The association with rs3130283 in AGPAT1 on chromosome 6 was observed in a meta-analysis of seven genome-wide association study (GWAS) datasets. Analysis of the full Wadi Ara GWAS dataset revealed 220 SNP associations with AD at p ≤ 10⁻⁵, and seven of these were confirmed in the replication GWAS datasets (p < 0.05). The unique population structure of Wadi Ara enhanced efforts to identify genetic variants that might partially explain the high prevalence of AD in the region. Several of these variants show modest evidence for association in other Caucasian populations.

Effect of the overexpression of mutant ubiquitin (K48R) on the cellular response induced by 4-hydroxy-2,3-trans-nonenal, an end-product of lipid peroxidation

Impairment of the ubiquitin-proteasome system (UPS) for degrading abnormal proteins leads to protein aggregates and increased protein oxidation/nitration. This study was performed to show that interference with polyubiquitination in the presence of 4-hydroxy-2,3-trans-nonenal (HNE) has similar consequences. Levels of polyubiquitin chains were not increased in NT-2 and SK-N-MC cells overexpressing a dominant-negative mutant form of ubiquitin (K48R) in response to HNE compared to wild-type transfectants. Increased oxidative (GSH, protein carbonyls and lipid peroxidation) and nitrative damage (nitric oxide production and elevated protein nitration) were aggravated in the mutant transfectants. These data show that initial oxidative/nitrative damage (due to HNE) and interference with ubiquitination (induced by mutant ubiquitin or HNE) can cause common characteristics of neurodegenerative diseases. These data suggest that impairment of the UPS at different levels may be a common mechanism in neurodegeneration and that more such defects remain to be identified.

Immunopositivity for ESCRT-III subunit CHMP2B in granulovacuolar degeneration of neurons in the Alzheimer's disease hippocampus

Endosomal sorting complex required for transport (ESCRT)-III subunit charged multivesicular body protein 2B (CHMP2B) is involved in the degradation of proteins in the endocytic and autophagic pathways. Mutations in the CHMP2B gene are reportedly associated with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) characterised by accumulation of ubiquitinated protein aggregates in affected neurons, suggesting a relationship between protein accumulation and efficient autophagic degradation. This study investigated CHMP2B immunoreactivity in the hippocampus of patients with Alzheimer's disease (AD), revealing intense labeling of intraneuronal dot-like structures by antibody to CHMP2B. Since the morphological characteristics of these granular structures were compatible with those of granulovacuolar degeneration (GVD), a hallmark of AD pathology, immunohistochemical study using anti-CHMP2B antibody was performed using AD and control brain sections to investigate whether this antibody can be used as a GVD label. The number and percentage of hippocampal neurons with CHMP2B-positive granules were higher in AD cases and CHMP2B-positive granules corresponded to GVD. Anti-CHMP2B antibody detected a single 28-kDa band on Western blotting using control and AD specimens. This antibody clearly and intensely detected GVD over the hippocampus and entorhinal and transentorhinal cortices. These findings suggest that researchers will be able to use CHMP2B as a molecular label for studying GVD.

Maintained activity of glycogen synthase kinase-3beta despite of its phosphorylation at serine-9 in okadaic acid-induced neurodegenerative model

Glycogen synthase kinase-3beta (GSK3beta) is recognized as one of major kinases to phosphorylate tau in Alzheimer's disease (AD), thus lots of AD drug discoveries target GSK3beta. However, the inactive form of GSK3beta which is phosphorylated at serine-9 is increased in AD brains. This is also inconsistent with phosphorylation status of other GSK3beta substrates, such as beta-catenin and collapsin response mediator protein-2 (CRMP2) since their phosphorylation is all increased in AD brains. Thus, we addressed this paradoxical condition of AD in rat neurons treated with okadaic acid (OA) which inhibits protein phosphatase-2A (PP2A) and induces tau hyperphosphorylation and cell death. Interestingly, OA also induces phosphorylation of GSK3beta at serine-9 and other substrates including tau, beta-catenin and CRMP2 like in AD brains. In this context, we observed that GSK3beta inhibitors such as lithium chloride and 6-bromoindirubin-3'-monoxime (6-BIO) reversed those phosphorylation events and protected neurons. These data suggest that GSK3beta may still have its kinase activity despite increase of its phosphorylation at serine-9 in AD brains at least in PP2A-compromised conditions and that GSK3beta inhibitors could be a valuable drug candidate in AD.

A common biological mechanism in cancer and Alzheimer's disease?

Cancer and Alzheimer's disease (AD) are two common disorders for which the final pathophysiological mechanism is not yet clearly defined. In a prospective longitudinal study we have previously shown an inverse association between AD and cancer, such that the rate of developing cancer in general with time was significantly slower in participants with AD, while participants with a history of cancer had a slower rate of developing AD. In cancer, cell regulation mechanisms are disrupted with augmentation of cell survival and/or proliferation, whereas conversely, AD is associated with increased neuronal death, either caused by, or concomitant with, beta amyloid (Abeta) and tau deposition. The possibility that perturbations of mechanisms involved in cell survival/death regulation could be involved in both disorders is discussed. Genetic polymorphisms, DNA methylation or other mechanisms that induce changes in activity of molecules with key roles in determining the decision to "repair and live"- or "die" could be involved in the pathogenesis of the two disorders. As examples, the role of p53, Pin1 and the Wnt signaling pathway are discussed as potential candidates that, speculatively, may explain inverse associations between AD and cancer.

Wnt signaling in Alzheimer's disease: up or down, that is the question

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, neuropathologically characterized by amyloid-beta (Abeta) plaques and hyperphosphorylated tau accumulation. AD occurs sporadically (SAD), or is caused by hereditary missense mutations in the amyloid precursor protein (APP) or presenilin-1 and -2 (PSEN1 and PSEN2) genes, leading to early-onset familial AD (FAD). Accumulating evidence points towards a role for altered Wnt/beta-catenin-dependent signaling in the etiology of both forms of AD. Presenilins are involved in modulating beta-catenin stability; therefore FAD-linked PSEN-mediated effects can deregulate the Wnt pathway. Genetic variations in the low-density lipoprotein receptor-related protein 6 and apolipoprotein E in AD have been associated with reduced Wnt signaling. In addition, tau phosphorylation is mediated by glycogen synthase kinase-3 (GSK-3), a key antagonist of the Wnt pathway. In this review, we discuss Wnt/beta-catenin signaling in both SAD and FAD, and recapitulate which of its aberrant functions may be critical for (F)AD pathogenesis. We discuss the intriguing possibility that Abeta toxicity may downregulate the Wnt/beta-catenin pathway, thereby upregulating GSK-3 and consequent tau hyperphosphorylation, linking Abeta and tangle pathology. The currently available evidence implies that disruption of tightly regulated Wnt signaling may constitute a key pathological event in AD. In this context, drug targets aimed at rescuing Wnt signaling may prove to be a constructive therapeutic strategy for AD.

The role of Wnt signaling in neuronal dysfunction in Alzheimer's Disease

Recent evidence supports a neuroprotective role for Wnt signaling in neurodegenerative disorders such as Alzheimer's Disease (AD). In fact, a relationship between amyloid-beta-peptide (Abeta)-induced neurotoxicity and a decrease in the cytoplasmic levels of beta-catenin has been observed. Apparently Abeta binds to the extracellular cysteine-rich domain of the Frizzled receptor (Fz) inhibiting Wnt/beta-catenin signaling. Cross-talk with other signaling cascades that regulate Wnt/beta-catenin signaling, including the activation of M1 muscarinic receptor and PKC, the use of Ibuprofen-ChE bi-functional compounds, PPAR alpha, gamma agonists, nicotine and some antioxidants, results in neuroprotection against Abeta. These studies indicate that a sustained loss of Wnt signaling function may be involved in the Abeta-dependent neurodegeneration observed in Alzheimer's brain. In conclusion the activation of the Wnt signaling pathway could be proposed as a therapeutic target for the treatment of AD.

The Wnt signaling pathway: aging gracefully as a protectionist?

No longer considered to be exclusive to cellular developmental pathways, the Wnt family of secreted cysteine-rich glycosylated proteins has emerged as versatile targets for a variety of conditions that involve cardiovascular disease, aging, cancer, diabetes, neurodegeneration, and inflammation. In particular, modulation of Wnt signaling may fill a critical void for the treatment of disorders that impact upon both cellular survival and cellular longevity. Yet, in some scenarios, Wnt signaling can become the catalyst for disease development or promote cell senescence that can compromise clinical utility. This double edge sword in regards to the role of Wnt and its signaling pathways highlights the critical need to further elucidate the cellular mechanisms governed by Wnt in conjunction with the development of robust pharmacological ligands that may open new avenues for disease treatment. Here we discuss the influence of the Wnt pathway during cell survival, metabolism, and aging in order for one to gain a greater insight for the novel role of Wnt signaling as well as exemplify its unique cellular pathways that influence both normal physiology and disease.

Amyloid precursor protein modulates beta-catenin degradation

Background

The amyloid precursor protein (APP) is genetically associated with Alzheimer's disease (AD). Elucidating the function of APP should help understand AD pathogenesis and provide insights into therapeutic designs against this devastating neurodegenerative disease.

Results

We demonstrate that APP expression in primary neurons induces β-catenin phosphorylation at Ser₃₃, Ser₃₇, and Thr₄₁ (S33/37/T41) residues, which is a prerequisite for β-catenin ubiquitinylation and proteasomal degradation. APP-induced phosphorylation of β-catenin resulted in the reduction of total β-catenin levels, suggesting that APP expression promotes β-catenin degradation. In contrast, treatment of neurons with APP siRNAs increased total β-catenin levels and decreased β-catenin phosphorylation at residues S33/37/T41. Further, β-catenin was dramatically increased in hippocampal CA1 pyramidal cells from APP knockout animals. Acute expression of wild type APP or of familial AD APP mutants in primary neurons downregulated β-catenin in membrane and cytosolic fractions, and did not appear to affect nuclear β-catenin or β-catenin-dependent transcription. Conversely, in APP knockout CA1 pyramidal cells, accumulation of β-catenin was associated with the upregulation of cyclin D1, a downstream target of β-catenin signaling. Together, these data establish that APP downregulates β-catenin and suggest a role for APP in sustaining neuronal function by preventing cell cycle reactivation and maintaining synaptic integrity.

Conclusion

We have provided strong evidence that APP modulates β-catenin degradation in vitro and in vivo. Future studies may investigate whether APP processing is necessary for β-catenin downregulation, and determine if excessive APP expression contributes to AD pathogenesis through abnormal β-catenin downregulation.

Presenilin 1 regulates epidermal growth factor receptor turnover and signaling in the endosomal-lysosomal pathway

Mutations in the gene encoding presenilin 1 (PS1) cause the most aggressive form of early-onset familial Alzheimer disease. In addition to its well established role in Abeta production and Notch proteolysis, PS1 has been shown to mediate other physiological activities, such as regulation of the Wnt/beta-catenin signaling pathway, modulation of phosphatidylinositol 3-kinase/Akt and MEK/ERK signaling, and trafficking of select membrane proteins and/or intracellular vesicles. In this study, we present evidence that PS1 is a critical regulator of a key signaling receptor tyrosine kinase, epidermal growth factor receptor (EGFR). Specifically, EGFR levels were robustly increased in fibroblasts deficient in both PS1 and PS2 (PS(-/-)) due to delayed turnover of EGFR protein. Stable transfection of wild-type PS1 but not PS2 corrected EGFR to levels comparable to PS(+/+) cells, while FAD PS1 mutations showed partial loss of activity. The C-terminal fragment of PS1 was sufficient to fully reduce EGFR levels. In addition, the rapid ligand-induced degradation of EGFR was markedly delayed in PS(-/-) cells, resulting in prolonged signal activation. Despite the defective turnover of EGFR, ligand-induced autophosphorylation, ubiquitination, and endocytosis of EGFR were not affected by the lack of PS1. Instead, the trafficking of EGFR from early endosomes to lysosomes was severely delayed by PS1 deficiency. Elevation of EGFR was also seen in brains of adult mice conditionally ablated in PS1 and in skin tumors associated with the loss of PS1. These findings demonstrate a critical role of PS1 in the trafficking and turnover of EGFR and suggest potential pathogenic effects of elevated EGFR as well as perturbed endosomal-lysosomal trafficking in cell cycle control and Alzheimer disease.

Relation of hippocampal phospho-SAPK/JNK granules in Alzheimer's disease and tauopathies to granulovacuolar degeneration bodies

Protein misfolding is a distinguishing feature of a number of neurodegenerative diseases. Accumulation of misfolded protein often results in cellular lesions, the location of lesions correlating with the nature of symptoms. Alzheimer's disease (AD), Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD) and Pick's Disease (PiD) all present with pathological lesions containing hyperphosphorylated filamentous tau protein; however, the location and type of lesion varies. In addition, granulovacuolar degeneration (GVD) bodies have been reported within hippocampal pyramidal neurons in AD, PSP, CBD and PiD tissue. GVDs are defined as electron-dense granules within double membrane-bound cytoplasmic vacuoles. We have previously reported that the phosphorylated form of stress-activated protein kinase/c-Jun N-terminal kinase (p-SAPK/JNK) accumulates in granules within hippocampal pyramidal cell bodies in AD tissue at the time that hyperphosphorylated tau begins to aggregate into early-stage NFTs. We now report that p-SAPK/JNK granules are found within the hippocampal CA1 region of PSP, CBD and PiD cases as well and that these granules are likely GVD bodies. Quantitatively, p-SAPK/JNK granules and GVDs are found in comparable numbers of CA1 cells. Within cells, p-SAPK/JNK granules are distributed throughout the cytoplasm in a manner similar to the distribution of GVDs and a subset of granules co-localize with GVD markers. Ultrastructurally, p-SAPK/JNK granules are located in large cytoplasmic vacuoles, thereby fitting the definition of a GVD body. With the implication of granular p-SAPK/JNK as a marker of GVDs, our study strongly suggests that a heterogeneous group of proteins form GVDs. The mechanism of GVD formation is therefore an interesting one, and is likely separate and distinct from the mechanism of tau inclusion formation.

Altered distributions of nucleocytoplasmic transport-related proteins in the spinal cord of a mouse model of amyotrophic lateral sclerosis

Recent investigations have indicated that the nucleocytoplasmic transport system is essential for maintaining cell viability and cellular functions and that its dysfunction could lead to certain disorders. To investigate the involvement of this system in the pathomechanisms of amyotrophic lateral sclerosis (ALS), we examined the immunohistochemical localization of proteins associated with nucleocytoplasmic transport in the lumbar spinal cord in a mutant SOD1 (G93A) transgenic mouse model of ALS. This model is widely used for ALS research, and the mutant mice are known to exhibit neuronal loss and Lewy body-like hyaline inclusions (LBHIs) in the anterior horns, similar to the pathology seen in familial ALS patients associated with an SOD1 mutation and in several other transgenic rodent models. Using antibodies against the importin beta family of proteins, the major carrier proteins of nucleocytoplasmic transport, and those against their adapter protein, importin alpha, we found that the immunoreactivities were decreased within the nuclei and increased within the cytoplasm of a subset of the surviving anterior horn cells of the transgenic mice. In addition, LBHIs were invariably reactive toward these antibodies. Furthermore, the immunoreactivities for histone H1 and beta-catenin, representative cargo proteins transported by importin beta-dependent and beta-independent nucleocytoplasmic transport pathways, respectively, showed distributions similar to those for importin beta family and importin alpha proteins. The altered distributions of these proteins were not associated with caspase-3 expression, suggesting that the findings are unlikely to be a manifestation of apoptotic processes. Chronological quantitative analysis of importin beta-immunostained sections from the transgenic mice revealed a statistically significant progressive decrease in the proportion of the anterior horn cells exhibiting a more intense reactivity for these proteins in the nucleus than in the cytoplasm. To the contrary, we found that the anterior horn cells with the immunoreactivity in their cytoplasm, being more pronounced than that in their nucleus, were significantly increased in number along with the disease progression. This is the first report investigating nucleocytoplasmic transport in the ALS model mouse, and our present results imply that its dysfunction could be involved in the pathomechanisms underlying ALS.

Casein kinase-1 isoforms differentially associate with neurofibrillary and granulovacuolar degeneration lesions

Alzheimer's Disease (AD) is characterized by the appearance of neurofibrillary and granulovacuolar lesions in the brains of affected individuals. The former is composed of hyperphosphorylated aggregates of the microtubule-associated protein tau. The latter is poorly characterized but reacts strongly with anti-phosphoepitope antibodies indicating that it too accumulates phosphoproteins. Both lesions react strongly with antibodies directed against members of the casein kinase-1 family of phosphotransferases, a group of closely related protein kinases that frequently function in tandem with the ubiquitin modification system. To determine whether individual members of the casein kinase-1 family differentially associate with AD lesions, hippocampal sections isolated from late stage cases of AD were subjected to double-label fluorescence immunohistochemistry using a panel of selective anti-casein kinase 1 antibodies and small-molecule fluorochromes thioflavin S and thiazin red. The resultant colocalization patterns revealed that the alpha CK1 isoform strongly correlated with thioflavin S and thiazin red fluorescence, indicating that it preferentially associated with neurofibrillary lesions. In contrast, the delta isoform staining pattern was dominated by colocalization with granulovacuolar degeneration bodies. These findings suggest that granulovacuolar and neurofibrillary lesions occupy separate populations of neurons, and implicate CK1 isoforms in the generation of lesion-associated phosphoepitopes. They also suggest a nexus between the phosphorylation and ubiquitination modifications found in both lesions.