Wnt signaling in vertebrate neural development and function

Association between maternal periconceptional alcohol consumption and neural tube defects: Findings from the National Birth Defects Prevention Study, 1997-2011

BACKGROUND

Neural tube defects (NTD)s are common birth defects with a multifactorial etiology. Findings from human studies examining environmental (non-inherited) exposures tend to be inconclusive. In particular, although animal studies of alcohol exposure and NTDs support its teratogenic potential, human studies are equivocal. Using data from the National Birth Defects Prevention Study (NBDPS), associations between maternal periconceptional (1 month before through 1 month after conception) alcohol consumption and NTDs in offspring were examined.

METHODS

NTD cases and unaffected live born singleton controls with expected dates of delivery from October 1997-December 2011 were enrolled in the NBDPS. Interview reports of alcohol consumption (quantity, frequency, variability, type) from 1,922 case and 11,251 control mothers were analyzed. Crude and adjusted odds ratios (aOR)s and 95% confidence intervals (CI)s for alcohol consumption and all NTDs combined and selected subtypes (spina bifida, anencephaly, encephalocele) were estimated using unconditional logistic regression analysis.

RESULTS

Among mothers in the NBDPS, 28% of NTD case and 35% of control mothers reported any periconceptional alcohol consumption. For each measure of alcohol consumption, inverse associations were observed for all NTDs combined (aORs = 0.6-1.0). Results for NTD subtypes tended to be similar, but CIs for spina bifida and encephalocele were more likely to include the null.

CONCLUSIONS

These findings suggest a lack of positive associations between maternal periconceptional alcohol consumption and NTDs. Future studies should continue to evaluate the association between maternal alcohol consumption and NTDs in offspring accounting for methodological limitations such as potential misclassification from self-reported alcohol consumption.

WNT3A Promotes Neuronal Regeneration upon Traumatic Brain Injury

The treatment of traumatic brain injury (TBI) remains a challenge due to limited knowledge about the mechanisms underlying neuronal regeneration. This current study compared the expression of WNT genes during regeneration of injured cortical neurons. Recombinant WNT3A showed positive effect in promoting neuronal regeneration via in vitro, ex vivo, and in vivo TBI models. Intranasal administration of WNT3A protein to TBI mice increased the number of NeuN⁺ neurons without affecting GFAP⁺ glial cells, compared to control mice, as well as retained motor function based on functional behavior analysis. Our findings demonstrated that WNT3A, 8A, 9B, and 10A promote regeneration of injured cortical neurons. Among these WNTs, WNT3A showed the most promising regenerative potential in vivo, ex vivo, and in vitro.

Systematic Identification of Cell-Cell Communication Networks in the Developing Brain

Since the generation of cell-type specific knockout models, the importance of inter-cellular communication between neural, vascular, and microglial cells during neural development has been increasingly appreciated. However, the extent of communication between these major cell populations remains to be systematically mapped. Here, we describe EMBRACE (embryonic brain cell extraction using FACS), a method to simultaneously isolate neural, mural, endothelial, and microglial cells to more than 94% purity in ∼4 h. Utilizing EMBRACE we isolate, transcriptionally analyze, and build a cell-cell communication map of the developing mouse brain. We identify 1,710 unique ligand-receptor interactions between neural, endothelial, mural, and microglial cells in silico and experimentally confirm the APOE-LDLR, APOE-LRP1, VTN-KDR, and LAMA4-ITGB1 interactions in the E14.5 brain. We provide our data via the searchable “Brain interactome explorer”, available at https://mpi-ie.shinyapps.io/braininteractomeexplorer/. Together, this study provides a comprehensive map that reveals the richness of communication within the developing brain.

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Isolation of embryonic neural, mural, endothelial, and microglial cells to >94% purity

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Transcriptome analyses of neural, vascular, and microglial cells from E14.5 brain

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Generation of inter-cellular communication network with 1,710 unique interactions

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Established “Brain interactome explorer,” a searchable cell communication database

A TBR1-K228E Mutation Induces Tbr1 Upregulation, Altered Cortical Distribution of Interneurons, Increased Inhibitory Synaptic Transmission, and Autistic-Like Behavioral Deficits in Mice

Mutations in Tbr1, a high-confidence ASD (autism spectrum disorder)-risk gene encoding the transcriptional regulator TBR1, have been shown to induce diverse ASD-related molecular, synaptic, neuronal, and behavioral dysfunctions in mice. However, whether Tbr1 mutations derived from autistic individuals cause similar dysfunctions in mice remains unclear. Here we generated and characterized mice carrying the TBR1-K228E de novo mutation identified in human ASD and identified various ASD-related phenotypes. In heterozygous mice carrying this mutation (Tbr1^+/K228E mice), levels of the TBR1-K228E protein, which is unable to bind target DNA, were strongly increased. RNA-Seq analysis of the Tbr1^+/K228E embryonic brain indicated significant changes in the expression of genes associated with neurons, astrocytes, ribosomes, neuronal synapses, and ASD risk. The Tbr1^+/K228E neocortex also displayed an abnormal distribution of parvalbumin-positive interneurons, with a lower density in superficial layers but a higher density in deep layers. These changes were associated with an increase in inhibitory synaptic transmission in layer 6 pyramidal neurons that was resistant to compensation by network activity. Behaviorally, Tbr1^+/K228E mice showed decreased social interaction, increased self-grooming, and modestly increased anxiety-like behaviors. These results suggest that the human heterozygous TBR1-K228E mutation induces ASD-related transcriptomic, protein, neuronal, synaptic, and behavioral dysfunctions in mice.

Molecular characterisation of a cellular conveyor belt in Clytia medusae

The tentacular system of Clytia hemisphaerica medusa (Cnidaria, Hydrozoa) has recently emerged as a promising experimental model to tackle the developmental mechanisms that regulate cell lineage progression in an early-diverging animal phylum. From a population of proximal stem cells, the successive steps of tentacle stinging cell (nematocyte) elaboration, are spatially ordered along a "cellular conveyor belt". Furthermore, the C. hemisphaerica tentacular system exhibits bilateral organisation, with two perpendicular polarity axes (proximo-distal and oral-aboral). We aimed to improve our knowledge of this cellular system by combining RNAseq-based differential gene expression analyses and expression studies of Wnt signalling genes. RNAseq comparisons of gene expression levels were performed (i) between the tentacular system and a control medusa deprived of all tentacles, nematogenic sites and gonads, and (ii) between three samples staggered along the cellular conveyor belt. The behaviour in these differential expression analyses of two reference gene sets (stem cell genes; nematocyte genes), as well as the relative representations of selected gene ontology categories, support the validity of the cellular conveyor belt model. Expression patterns obtained by in situ hybridisation for selected highly differentially expressed genes and for Wnt signalling genes are largely consistent with the results from RNAseq. Wnt signalling genes exhibit complex spatial deployment along both polarity axes of the tentacular system, with the Wnt/β-catenin pathway probably acting along the oral-aboral axis rather than the proximo-distal axis. These findings reinforce the idea that, despite overall radial symmetry, cnidarians have a full potential for elaboration of bilateral structures based on finely orchestrated deployment of an ancient developmental gene toolkit.

WNT Signaling in Disease

Developmental signaling pathways control a vast array of biological processes during embryogenesis and in adult life. The WNT pathway was discovered simultaneously in cancer and development. Recent advances have expanded the role of WNT to a wide range of pathologies in humans. Here, we discuss the WNT pathway and its role in human disease and some of the advances in WNT-related treatments.

ADNP differentially interact with genes/proteins in correlation with aging: a novel marker for muscle aging

Activity-dependent neuroprotective protein (ADNP) is essential for embryonic development with ADNP mutations leading to syndromic autism, coupled with intellectual disabilities and motor developmental delays. Here, mining human muscle gene-expression databases, we have investigated the association of ADNP transcripts with muscle aging. We discovered increased ADNP and its paralogue ADNP2 expression in the vastus lateralis muscle of aged compared to young subjects, as well as altered expression of the ADNP and the ADNP2 genes in bicep brachii muscle of elderly people, in a sex-dependent manner. Prolonged exercise resulted in decreased ADNP expression, and increased ADNP2 expression in an age-dependent manner in the vastus lateralis muscle. ADNP expression level was further correlated with 49 genes showing age-dependent changes in muscle transcript expression. A high degree of correlation with ADNP was discovered for 24 genes with the leading gene/protein being NMNAT1 (nicotinamide nucleotide adenylyl transferase 1). Looking at correlations differentiating the young and the old muscles and comparing protein interactions revealed an association of ADNP with the cell division cycle 5-like protein (CDC5L), and an aging-muscle-related interactive pathway in the vastus lateralis. In the bicep brachii, very high correlation was detected with genes associated with immune functions as well as mitochondrial structure and function among others. Taken together, the results suggest a direct association of ADNP with muscle strength and implicate ADNP fortification in the protection against age-associated muscle wasting.

Low-frequency variation in TP53 has large effects on head circumference and intracranial volume

Cranial growth and development is a complex process which affects the closely related traits of head circumference (HC) and intracranial volume (ICV). The underlying genetic influences shaping these traits during the transition from childhood to adulthood are little understood, but might include both age-specific genetic factors and low-frequency genetic variation. Here, we model the developmental genetic architecture of HC, showing this is genetically stable and correlated with genetic determinants of ICV. Investigating up to 46,000 children and adults of European descent, we identify association with final HC and/or final ICV + HC at 9 novel common and low-frequency loci, illustrating that genetic variation from a wide allele frequency spectrum contributes to cranial growth. The largest effects are reported for low-frequency variants within TP53, with 0.5 cm wider heads in increaser-allele carriers versus non-carriers during mid-childhood, suggesting a previously unrecognized role of TP53 transcripts in human cranial development.

Expanding the Spectrum of BAF-Related Disorders: De Novo Variants in SMARCC2 Cause a Syndrome with Intellectual Disability and Developmental Delay

SMARCC2 (BAF170) is one of the invariable core subunits of the ATP-dependent chromatin remodeling BAF (BRG1-associated factor) complex and plays a crucial role in embryogenesis and corticogenesis. Pathogenic variants in genes encoding other components of the BAF complex have been associated with intellectual disability syndromes. Despite its significant biological role, variants in SMARCC2 have not been directly associated with human disease previously. Using whole-exome sequencing and a web-based gene-matching program, we identified 15 individuals with variable degrees of neurodevelopmental delay and growth retardation harboring one of 13 heterozygous variants in SMARCC2, most of them novel and proven de novo. The clinical presentation overlaps with intellectual disability syndromes associated with other BAF subunits, such as Coffin-Siris and Nicolaides-Baraitser syndromes and includes prominent speech impairment, hypotonia, feeding difficulties, behavioral abnormalities, and dysmorphic features such as hypertrichosis, thick eyebrows, thin upper lip vermilion, and upturned nose. Nine out of the fifteen individuals harbor variants in the highly conserved SMARCC2 DNA-interacting domains (SANT and SWIRM) and present with a more severe phenotype. Two of these individuals present cardiac abnormalities. Transcriptomic analysis of fibroblasts from affected individuals highlights a group of differentially expressed genes with possible roles in regulation of neuronal development and function, namely H19, SCRG1, RELN, and CACNB4. Our findings suggest a novel SMARCC2-related syndrome that overlaps with neurodevelopmental disorders associated with variants in BAF-complex subunits.

Single-cell RNA-seq reveals dynamic transcriptome profiling in human early neural differentiation

Background

Investigating cell fate decision and subpopulation specification in the context of the neural lineage is fundamental to understanding neurogenesis and neurodegenerative diseases. The differentiation process of neural-tube-like rosettes in vitro is representative of neural tube structures, which are composed of radially organized, columnar epithelial cells and give rise to functional neural cells. However, the underlying regulatory network of cell fate commitment during early neural differentiation remains elusive.

Results

In this study, we investigated the genome-wide transcriptome profile of single cells from six consecutive reprogramming and neural differentiation time points and identified cellular subpopulations present at each differentiation stage. Based on the inferred reconstructed trajectory and the characteristics of subpopulations contributing the most toward commitment to the central nervous system lineage at each stage during differentiation, we identified putative novel transcription factors in regulating neural differentiation. In addition, we dissected the dynamics of chromatin accessibility at the neural differentiation stages and revealed active cis-regulatory elements for transcription factors known to have a key role in neural differentiation as well as for those that we suggest are also involved. Further, communication network analysis demonstrated that cellular interactions most frequently occurred in the embryoid body stage and that each cell subpopulation possessed a distinctive spectrum of ligands and receptors associated with neural differentiation that could reflect the identity of each subpopulation.

Conclusions

Our study provides a comprehensive and integrative study of the transcriptomics and epigenetics of human early neural differentiation, which paves the way for a deeper understanding of the regulatory mechanisms driving the differentiation of the neural lineage.

Insulin-like growth factor binding protein 4 inhibits proliferation of bone marrow mesenchymal stem cells and enhances growth of neurospheres derived from the stem cells

Insulin-like growth factor binding protein 4 (IGFBP-4) was reported to trigger cellular senescence and reduce cell growth of bone marrow mesenchymal stem cells (BMSCs), but its contribution to neurogenic differentiation of BMSCs remains unknown. In the present study, BMSCs were isolated from the femur and tibia of young rats to investigate effects of IGFBP-4 on BMSC proliferation and growth of neurospheres derived from BMSCs. Bone marrow mesenchymal stem cell proliferation was assessed using CCK-8 after treatment with IGFBP-4 or blockers of IGF-IR and β-catenin. Phosphorylation levels of Akt, Erk, and p38 in BMSCs were analysed by Western blotting. Bone marrow mesenchymal stem cells were induced into neural lineages in NeuroCult medium; the number and the size of BMSC-derived neurospheres were counted after treatment with IGFBP-4 or the blockers. It was shown that addition of IGFBP-4 inhibited BMSC proliferation and immunodepletion of IGFBP-4 increased the proliferation. The blockade of IGF-IR with AG1024 increased BMSC proliferation and reversed IGFBP-4-induced proliferation inhibition; however, blocking of β-catenin with FH535 did not. p-Erk was significantly decreased in IGFBP-4-treated BMSCs. IGFBP-4 promoted the growth of neurospheres derived from BMSCs, as manifested by the increases in the number and the size of the derived neurospheres. Both AG1024 and FH535 inhibited the formation of NeuroCult-induced neurospheres, but FH535 significantly inhibited the growth of neurospheres in NeuroCult medium with EGF, bFGF, and IGFBP-4. The data suggested that IGFBP-4 inhibits BMSC proliferation through IGF-IR pathway and promotes growth of BMSC-derived neurospheres via stabilizing β-catenin.

Wnt/β-catenin signaling as a potential target for novel epilepsy therapies

Epilepsy is one of the most common neurological disorders, and yet many afflicted individuals are resistant to all available therapeutic treatments. Existing pharmaceutical treatments function primarily to reduce hyperexcitability and prevent seizures, but fail to influence the underlying pathophysiology of the disorder. Recently, research efforts have focused on identifying alternative mechanistic targets for anti-epileptogenic therapies that can prevent the development of chronic epilepsy. The Wnt/β-catenin pathway, one possible target, has been demonstrated to be disrupted in both acute and chronic phases of epilepsy. Wnt/β-catenin signaling can regulate many seizure-induced changes in the brain, including neurogenesis and neuronal death, as well as can influence seizure susceptibility and potentially the development of chronic epilepsy. Several genome-wide studies and in vivo knockout animal models have provided evidence for an association between disrupted Wnt/β-catenin signaling and epilepsy. Furthermore, approved pharmaceutical drugs and other small molecule compounds that target components of the β-catenin destruction complex or antagonize endogenous inhibitors of the pathway have shown to be protective following seizures. However, additional studies are needed to determine the optimal time period in which modulation of the pathway may be most beneficial. Overall, disrupted molecular networks such as Wnt/β-catenin signaling, could be a promising anti-epileptogenic target for future epilepsy therapies.

Mid-gestational sevoflurane exposure inhibits fetal neural stem cell proliferation and impairs postnatal learning and memory function in a dose-dependent manner

Advancements in fetal intervention procedures have led to increases in the number of pregnant women undergoing general anesthesia during the second trimester-a period characterized by extensive proliferation of fetal neural stem cells (NSCs). However, few studies have investigated the effects of mid-gestational sevoflurane exposure on fetal NSC proliferation or postnatal learning and memory function. In the present study, pregnant rats were randomly assigned to a control group (C group), a low sevoflurane concentration group (2%; L group), a high sevoflurane concentration group (3.5%; H group), a high sevoflurane concentration plus lithium chloride group (H + Li group), and a lithium chloride group (Li group) at gestational day 14. Rats received different concentrations of sevoflurane anesthesia for 2 h. The offspring rats were weaned at 28 days for behavioral testing (i.e., Morris Water Maze [MWM]), and fetal brains or postnatal hippocampal tissues were harvested for immunofluorescence staining, real-time PCR, and Western blotting analyses in order to determine the effect of sevoflurane exposure on NSC proliferation and the Wnt/β-catenin signaling pathway. Our results indicated that maternal exposure to 3.5% sevoflurane (H group) during the mid-gestational period impaired the performance of offspring rats in the MWM test, reduced NSC proliferation, and increased protein levels of fetal glycogen synthase kinase-3 beta (GSK-3β). Such treatment also decreased levels of β-catenin protein, CD44 RNA, and Cyclin D1 RNA relative to those observed in the C group. However, these effects were transiently attenuated by treatment with lithium chloride. Conversely, maternal exposure to 2% sevoflurane (L group) did not influence NSC proliferation or the Wnt signaling pathway. Our results suggest that sevoflurane exposure during the second trimester inhibits fetal NSC proliferation via the Wnt/β-catenin pathway and impairs postnatal learning and memory function in a dose-dependent manner.

DIXDC1 contributes to psychiatric susceptibility by regulating dendritic spine and glutamatergic synapse density via GSK3 and Wnt/β-catenin signaling

Mice lacking DIX domain containing-1 (DIXDC1), an intracellular Wnt/β-catenin signal pathway protein, have abnormal measures of anxiety, depression and social behavior. Pyramidal neurons in these animals' brains have reduced dendritic spines and glutamatergic synapses. Treatment with lithium or a glycogen synthase kinase-3 (GSK3) inhibitor corrects behavioral and neurodevelopmental phenotypes in these animals. Analysis of DIXDC1 in over 9000 cases of autism, bipolar disorder and schizophrenia reveals higher rates of rare inherited sequence-disrupting single-nucleotide variants (SNVs) in these individuals compared with psychiatrically unaffected controls. Many of these SNVs alter Wnt/β-catenin signaling activity of the neurally predominant DIXDC1 isoform; a subset that hyperactivate this pathway cause dominant neurodevelopmental effects. We propose that rare missense SNVs in DIXDC1 contribute to psychiatric pathogenesis by reducing spine and glutamatergic synapse density downstream of GSK3 in the Wnt/β-catenin pathway.

Systematic Analysis of mRNA and miRNA Expression of 3D-Cultured Neural Stem Cells (NSCs) in Spaceflight

Recently, with the development of the space program there are growing concerns about the influence of spaceflight on tissue engineering. The purpose of this study was thus to determine the variations of neural stem cells (NSCs) during spaceflight. RNA-Sequencing (RNA-Seq) based transcriptomic profiling of NSCs identified many differentially expressed mRNAs and miRNAs between space and earth groups. Subsequently, those genes with differential expression were subjected to bioinformatic evaluation using gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) and miRNA-mRNA network analyses. The results showed that NSCs maintain greater stemness ability during spaceflight although the growth rate of NSCs was slowed down. Furthermore, the results indicated that NSCs tended to differentiate into neuron in outer space conditions. Detailed genomic analyses of NSCs during spaceflight will help us to elucidate the molecular mechanisms behind their differentiation and proliferation when they are in outer space.

Down-regulation of the Wnt/β-catenin signaling pathway by Cacnb4

The β4 isoform of the β-subunits of voltage-gated calcium channel regulates cell proliferation and cell cycle progression. Herein we show that coexpression of the β4-subunit with actors of the canonical Wnt/β-catenin signaling pathway in a hepatoma cell line inhibits Wnt-responsive gene transcription and decreases cell division, in agreement with the role of the Wnt pathway in cell proliferation. β4-subunit-mediated inhibition of Wnt signaling is observed in the presence of LiCl, an inhibitor of glycogen synthase kinase (GSK3) that promotes β-catenin translocation to the nucleus. Expression of β4-subunit mutants that lost the ability to translocate to the nucleus has no effect on Wnt signaling, suggesting that β4-subunit inhibition of Wnt signaling occurs downstream from GSK3 and requires targeting of β4-subunit to the nucleus. β4-subunit coimmunoprecipitates with the TCF4 transcription factor and overexpression of TCF4 reverses the effect of β4-subunit on the Wnt pathway. We thus propose that the interaction of nuclear β4-subunit with TCF4 prevents β-catenin binding to TCF4 and leads to the inhibition of the Wnt-responsive gene transcription. Thereby, our results show that β4-subunit is a TCF4 repressor and therefore appears as an interesting candidate for the regulation of this pathway in neurons where β4-subunit is specifically expressed.

Integrating molecular and structural findings: Wnt as a possible actor in shaping cognitive impairment in Cornelia de Lange syndrome

Cornelia de Lange Syndrome (CdLS) is a choesinopathy: a severe genetic disorder caused by mutations in the cohesin complex genes. The phenotype is characterized by typical facial dysmorphism, growth impairment and multiorgan abnormalities including brain alterations. Wnt pathway is known to play a fundamental role in central nervous system development and it has been shown that Wnt pathway is disrupted in CdLS animal models and patients cells. In this review we investigate the possible link between Wnt pathway disruption and brain abnormalities in Cornelia de Lange Syndrome as such molecular impairment could lead to an abnormal embryonic development resulting in brain abnormalities (i.e. microcephaly, cerebellar hypoplasia, abnormal cortical development) in patients with Cornelia de Lange Syndrome.

Targeting WNT Signaling for Multifaceted Glioblastoma Therapy

The WNT signaling pathway has been of great interest to developmental biologists for decades and has more recently become a central topic for study in cancer biology. It is vital for cell growth and regulation of embryogenesis in many organ systems, particularly the CNS and its associated vasculature. We summarize the role of WNT in CNS development and describe how WNT signaling makes key contributions to malignant glioma stemness, invasiveness, therapeutic resistance, and angiogenesis. The role of WNT in these mechanisms, along with creation and maintainance of the blood-brain barrier (BBB), points to the potential of WNT as a multi-faceted target in malignant glioma therapy.

Wnt/β-catenin signaling pathway inhibits the proliferation and apoptosis of U87 glioma cells via different mechanisms

The Wnt signaling pathway is necessary for the development of the central nervous system and is associated with tumorigenesis in various cancers. However, the mechanism of the Wnt signaling pathway in glioma cells has yet to be elucidated. Small-molecule Wnt modulators such as ICG-001 and AZD2858 were used to inhibit and stimulate the Wnt/β-catenin signaling pathway. Techniques including cell proliferation assay, colony formation assay, Matrigel cell invasion assay, cell cycle assay and Genechip microarray were used. Gene Ontology Enrichment Analysis and Gene Set Enrichment Analysis have enriched many biological processes and signaling pathways. Both the inhibiting and stimulating Wnt/β-catenin signaling pathways could influence the cell cycle, moreover, reduce the proliferation and survival of U87 glioma cells. However, Affymetrix expression microarray indicated that biological processes and networks of signaling pathways between stimulating and inhibiting the Wnt/β-catenin signaling pathway largely differ. We propose that Wnt/β-catenin signaling pathway might prove to be a valuable therapeutic target for glioma.

WNT/β-Catenin Pathway and Epigenetic Mechanisms Regulate the Pitt-Hopkins Syndrome and Schizophrenia Risk Gene

Genetic variation within the transcription factor TCF4 locus can cause the intellectual disability and developmental disorder Pitt-Hopkins syndrome (PTHS), whereas single-nucleotide polymorphisms within noncoding regions are associated with schizophrenia. These genetic findings position TCF4 as a link between transcription and cognition; however, the neurobiology of TCF4 remains poorly understood. Here, we quantitated multiple distinct TCF4 transcript levels in human induced pluripotent stem cell-derived neural progenitors and differentiated neurons, and PTHS patient fibroblasts. We identify two classes of pharmacological treatments that regulate TCF4 expression: WNT pathway activation and inhibition of class I histone deacetylases. In PTHS fibroblasts, both of these perturbations upregulate a subset of TCF4 transcripts. Finally, using chromatin immunoprecipitation sequencing in conjunction with genome-wide transcriptome analysis, we identified TCF4 target genes that may mediate the effect of TCF4 loss on neuroplasticity. Our studies identify new pharmacological assays, tools, and targets for the development of therapeutics for cognitive disorders.

Aberrant Wnt signaling: a special focus in CNS diseases

Wnt signals regulate cell proliferation, migration and differentiation during development, as well as synaptic transmission and plasticity in the adult brain. Abnormal Wnt signaling is central to a number of brain pathologies. We review here, the significance of this pathway focused in the contribution of the most frequent alterations in receptors, secretable modulators and downstream targets in Alzheimer's disease (AD) and Glioblastoma (GBM). β-catenin and GSK3 levels are pivotal in the neurodegeneration associated to AD contributing to memory deficits, tau phosphorylation, increased β-amyloid production and modulation of Apolipoprotein E in the brain. In consequence, β-catenin and GSK3 are targets for potential treatments in AD. Also, Wnt pathway components and secreted molecules interfering with this signaling contribute to the progression of tumoral cells. Wnt pathway activation is a bad prognosis in brain cancer; however, mutations in WNT or Frizzled (FZD) genes do not account for the cases of GBM. Instead, recent studies indicate that epigenetic modifications contribute to the development of GBMs opening novel strategies to study GBM progression.

Plasma dickkopf-related protein 1, an antagonist of the Wnt pathway, is associated with HIV-associated neurocognitive impairment

OBJECTIVE

Dickkopf-related protein 1 (DKK1) is a soluble antagonist of the Wningless (Wnt) pathway. It binds to and sequesters low-density lipoprotein receptor-related proteins 5/6 away from Wnts. Because the Wnt pathway regulates synaptic transmission and plasticity, we hypothesized that increased DKK1 would increase the risk for neurocognitive impairment (NCI) in HIV-positive (HIV) individuals. We evaluated, here, the relationship between plasma DKK1 and global NCI.

METHODS

Plasma samples and data from 41 HIV to 42 HIV adults were obtained from the University of California, San Diego, California, USA. Concentrations of DKK1 and a comparator protein, monocyte chemoattractant protein-1 (MCP-1), were quantified in plasma by immunoassay. All study participants completed a standardized comprehensive neuropsychological test battery and their performance was summarized using the global deficit score method.

RESULTS

A higher DKK1 level was associated with NCI among HIV participants (d = 0.63, P = 0.05), particularly among the 26 participants whose plasma HIV RNA level was suppressed (d = 0.74, P = 0.08). DKK1 level was not associated with NCI among HIV participants (P = 0.98). was not associated with NCI in either group. In HIV adults with suppressed plasma HIV RNA, a receiver operator characteristic curve identified that a DKK1 level of at least 735 pg/ml had a positive predictive value of 83.3% for a diagnosis of NCI. This association did not weaken after accounting for the effect of AIDS, nadir CD4 T-cell count, addictive drug use, or demographic characteristics.

CONCLUSION

DKK1 is a specific biomarker for NCI in HIV adults, implicating the Wnt pathway in HIV neuropathogenesis.

Regulation of WNT Signaling at the Neuromuscular Junction by the Immunoglobulin Superfamily Protein RIG-3 in Caenorhabditis elegans

Perturbations in synaptic function could affect the normal behavior of an animal, making it important to understand the regulatory mechanisms of synaptic signaling. Previous work has shown that in Caenorhabditis elegans an immunoglobulin superfamily protein, RIG-3, functions in presynaptic neurons to maintain normal acetylcholine receptor levels at the neuromuscular junction (NMJ). In this study, we elucidate the molecular and functional mechanism of RIG-3. We demonstrate by genetic and BiFC (Bi-molecular Fluorescence Complementation) assays that presynaptic RIG-3 functions by directly interacting with the immunoglobulin domain of the nonconventional Wnt receptor, ROR receptor tyrosine kinase (RTK), CAM-1, which functions in postsynaptic body-wall muscles. This interaction in turn inhibits Wnt/LIN-44 signaling through the ROR/CAM-1 receptor, and allows for maintenance of normal acetylcholine receptor, AChR/ACR-16, levels at the neuromuscular synapse. Further, this work reveals that RIG-3 and ROR/CAM-1 function through the β-catenin/HMP-2 at the NMJ. Taken together, our results demonstrate that RIG-3 functions as an inhibitory molecule of the Wnt/LIN-44 signaling pathway through the RTK, CAM-1.

Nanoparticulate TiO2 -mediated inhibition of the Wnt signaling pathway causes dendritic development disorder in cultured rat hippocampal neurons

Titanium dioxide nanoparticles (TiO₂ NPs) are increasingly used in daily life, in industry, and in environmental clearing, but their potential neurodevelopmental toxicity has been highly debated. In this study, we explored whether TiO₂ NPs inhibited development of dendritic morphology and identified possible molecular mechanisms associated with this inhibition in primary cultured rat hippocampal neurons. Results showed that TiO₂ NPs decreased neurite length, the number of branches and the spine density, and impaired mitochondrial function in the developing neurons. Furthermore, TiO₂ NPs significantly reduced the expression of several proteins involved in canonical Wnt3a/β-catenin signaling including Wnt3a, β-catenin, p-GSK-3β, and CyclinD1 and conversely, elevated GSK-3β expression. In addition to altering expression of proteins involved in canonical Wnt3a/β-catenin signaling, TiO₂ NPs decreased expression of proteins invovled in non-canonical Wnt signaling, including, MKLP1, CRMP3, ErbB4, and KIF17. Taken together, these results indicate that suppression of dendritic development caused by TiO₂ NPs is associated with inhibition of activation of the Wnt/β-catenin pathway or non-canonical Wnt pathway-induced expression of microtubule cytoskeletal components in the developing neurons. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2139-2149, 2017.

Interactions between canonical Wnt signaling pathway and MAPK pathway regulate differentiation, maturation and function of dendritic cells

Antigen-presenting dendritic cells interpret environmental signals to orchestrate local and systemic immune responses. In this study, the roles of Wnt proteins and their signaling pathway members in the maturation and function of monocyte-derived DCs were investigated. The present study showed higher expression of β-catenin, as well as pGSK-3β in DCs than those in monocytes. Wnt3a, Wnt5a and inhibition of GSK-3β promoted differentiation of DCs, but inhibited maturation of DCs. GSK-3β induced DCs maturation with unconventional phenotypes. Together with β-catenin silence, these treatment lead to reduced secretion of cytokines and chemokines except for IL-10 in comparison with LPS treatment, and significantly promoted proliferation of T cells. Wnt3a and inhibition of GSK-3β increased expression of MAPK signalings (p-ERK, p-p38, p-JNK). However, inhibition of MAPK signalings in turn differently regulated Wnt signaling proteins expression. These data suggest that Wnt pathway regulates DCs differentiation, maturation and function with interaction of MAPK signaling pathways.

Analysis of the expression of the Wnt family of proteins and its modulatory role on cytokine expression in non activated and activated astroglial cells

Despite the essential functions of astrocytes and the emerging relevance of the Wnt family of proteins in the CNS under physiological and pathological conditions, the astroglial expression of this family of proteins and its potential modulatory role on astroglial activation is almost unknown. Thus, we have evaluated the expression of all Wnt ligands, receptors and regulators, and the activation state of Wnt-related signaling pathways in non-activated and differentially activated astroglial cultures. We found that numerous Wnt ligands, receptors and regulators were expressed in non-activated astrocytes, while the Wnt-dependent pathways were constitutively active. Moreover, the expression of most detectable Wnt-related molecules and the activity of the Wnt-dependent pathways suffered post-activation variations which frequently depended on the activation system. Finally, the analysis of the effects exerted by Wnt1 and 5a on the astroglial expression of prototypical genes related to astroglial activation showed that both Wnt ligands increased the astroglial expression of interleukin 1β depending on the experimental context, while did not modulate tumor necrosis factor α, interleukin 6, transforming growth factor β1 and glial fibrillary acidic protein expression. These results strongly suggest that the Wnt family of proteins is involved in how astrocytes modulate and respond to the physiological and pathological CNS.

Claulansine F promoted the neuronal differentiation of neural stem and progenitor cells through Akt/GSK-3β/β-catenin pathway

The persistence of neurogenesis raises the idea that neurons produced by the resident or transplanted neural stem cells could replace the neurons lost from brain injury or neurodegenerative disease. Therefore, compounds or methods for promoting neuronal differentiation become the focus of neurodegenerative disease therapy research. Claulansine F (Clau F), a newly discovered carbazole alkaloid, has been showed to induce neuritogenesis in PC12 cells. Herein, we studied the effect of Clau F on neuronal differentiation of neural stem/progenitor cells (NS/PCs). The current study demonstrated that Clau F initiated neuronal differentiation with a significant increase of TuJ1-positive cells and TuJ1 protein levels. We also found that Clau F promoted the maturity and sustainability of neurons by increasing MAP2-positive cells and MAP2 protein levels. At the same time, Clau F significantly inhibited the proliferation of NS/PCs. The underlying mechanism of Clau F was preliminary explored. Clau F treatment resulted in a profound increase of phosphorylation of Akt and GSK-3β, which led to GSK-3β inhibition and subsequently the nuclear accumulation of β-catenin. Further, the interaction between β-catenin and p300 in the nucleus was enhanced and the transcription of p300/β-catenin responsive genes were increased significantly (c-jun, fra-1) by Clau F. Importantly, the positive effect of Clau F on neuronal differentiation was abolished by Akti-1/2, a specific inhibitor of Akt-1/2 kinase, which indicated the involvement of Akt/GSK-3β in Clau F-mediated neuronal differentiation. In conclusion, these data suggested that Clau F promoted neuronal differentiation through Akt/GSK-3β/β-catenin signaling pathway in NS/PCs.

Abnormal epigenetic regulation of the gene expression levels of Wnt2b and Wnt7b: Implications for neural tube defects

The association between Wnt genes and neural tube defects (NTDs) is recognized, however, it remains to be fully elucidated. Our previous study demonstrated that epigenetic mechanisms are affected in human NTDs. Therefore, the present study aimed to evaluate whether Wnt2b and Wnt7b are susceptible to abnormal epigenetic modification in NTDs, using chromatin immunoprecipitation assays to evaluate histone enrichments and the MassARRAY platform to detect the methylation levels of target regions within Wnt genes. The results demonstrated that the transcriptional activities of Wnt2b and Wnt7b were abnormally upregulated in mouse fetuses with NTDs and, in the GC-rich promoters of these genes, histone 3 lysine 4 (H3K4) acetylation was enriched, whereas H3K27 trimethylation was reduced. Furthermore, several CpG sites in the altered histone modification of target regions were significantly hypomethylated. The present study also detected abnormal epigenetic modifications of these Wnt genes in human NTDs. In conclusion, the present study detected abnormal upregulation in the levels of Wnt2b and Wnt7b, and hypothesized that the alterations may be due to the ectopic opening of chromatin structure. These results improve understanding of the dysregulation of epigenetic modification of Wnt genes in NTDs.

The Wnt and Notch signalling pathways in the developing cochlea: Formation of hair cells and induction of regenerative potential

The Wnt and Notch signalling pathways control proliferation, specification, and cell fate choices during embryonic development and in adult life. Hence, there is much interest in both signalling pathways in the context of stem cell biology and tissue regeneration. In the developing ear, the Wnt and Notch signalling pathways specify otic cells and refine the ventral boundary of the otic placode. Since both signalling pathways control events essential for the formation of sensory cells, such as proliferation and hair cell differentiation, these pathways could hold promise for the regeneration of hair cells in adult mammalian cochlea. Indeed, modulating either the Wnt or Notch pathways can trigger the regenerative potential of supporting cells. In the neonatal mouse cochlea, Notch-mediated regeneration of hair cells partially depends on Wnt signalling, which implies an interaction between the pathways. This review presents how the Wnt and Notch signalling pathways regulate the formation of sensory hair cells and how modulating their activity induces regenerative potential in the mammalian cochlea.

Dissecting the role of Wnt signaling and its interactions with FGF signaling during midbrain neurogenesis

Interactions between FGF and Wnt/ bcat signaling control development of the midbrain. The nature of this interaction and how these regulate patterning, growth and differentiation is less clear, as it has not been possible to temporally dissect the effects of one pathway relative to the other. We have employed pharmacological and genetic tools to probe the temporal and spatial roles of FGF and Wnt in controlling the specification of early midbrain neurons. We identify a β-catenin (bcat) independent role for GSK-3 in modulating FGF activity and hence neuronal patterning. This function is complicated by an overlap with bcat-dependent regulation of FGF signaling, through the regulation of sprouty4. Additionally we reveal how attenuation of Axin protein function can promote fluctuating levels of bcat activity that are dependent on FGF activity. This highlights the complex nature of the interactions between FGF and Wnt/ bcat and reveals that they act at multiple levels to control each others activity in the midbrain.

Wnt Signalling Promotes Actin Dynamics during Axon Remodelling through the Actin-Binding Protein Eps8

Upon arrival at their synaptic targets, axons slow down their growth and extensively remodel before the assembly of presynaptic boutons. Wnt proteins are target-derived secreted factors that promote axonal remodelling and synaptic assembly. In the developing spinal cord, Wnts secreted by motor neurons promote axonal remodelling of NT-3 responsive dorsal root ganglia neurons. Axon remodelling induced by Wnts is characterised by growth cone pausing and enlargement, processes that depend on the re-organisation of microtubules. However, the contribution of the actin cytoskeleton has remained unexplored. Here, we demonstrate that Wnt3a regulates the actin cytoskeleton by rapidly inducing F-actin accumulation in growth cones from rodent DRG neurons through the scaffold protein Dishevelled-1 (Dvl1) and the serine-threonine kinase Gsk3β. Importantly, these changes in actin cytoskeleton occurs before enlargement of the growth cones is evident. Time-lapse imaging shows that Wnt3a increases lamellar protrusion and filopodia velocity. In addition, pharmacological inhibition of actin assembly demonstrates that Wnt3a increases actin dynamics. Through a yeast-two hybrid screen, we identified the actin-binding protein Eps8 as a direct interactor of Dvl1, a scaffold protein crucial for the Wnt signalling pathway. Gain of function of Eps8 mimics Wnt-mediated axon remodelling, whereas Eps8 silencing blocks the axon remodelling activity of Wnt3a. Importantly, blockade of the Dvl1-Eps8 interaction completely abolishes Wnt3a-mediated axonal remodelling. These findings demonstrate a novel role for Wnt-Dvl1 signalling through Eps8 in the regulation of axonal remodeling.

Canonical wnt signaling is required for commissural axon guidance

Morphogens have been identified as guidance cues for postcrossing commissural axons in the spinal cord. Shh has a dual effect on postcrossing commissural axons: a direct repellent effect mediated by Hhip as a receptor, and an indirect effect by shaping a Wnt activity gradient. Wnts were shown to be attractants for postcrossing commissural axons in both chicken and mouse embryos. In mouse, the effects of Wnts on axon guidance were concluded to depend on the planar cell polarity (PCP) pathway. Canonical Wnt signaling was excluded based on the absence of axon guidance defects in mice lacking Lrp6 which is an obligatory coreceptor for Fzd in canonical Wnt signaling. In the loss-of-function studies reported here, we confirmed a role for the PCP pathway in postcrossing commissural axon guidance also in the chicken embryo. However, taking advantage of the precise temporal control of gene silencing provided by in ovo RNAi, we demonstrate that canonical Wnt signaling is also required for proper guidance of postcrossing commissural axons in the developing spinal cord. Thus, axon guidance does not seem to depend on any one of the classical Wnt signaling pathways but rather involve a network of Wnt receptors and downstream components.

microRNA regulation of Wnt signaling pathways in development and disease

Wnt signaling pathways and microRNAs (miRNAs) are critical regulators of development. Aberrant Wnt signaling pathways and miRNA levels lead to developmental defects and diverse human pathologies including but not limited to cancer. Wnt signaling pathways regulate a plethora of cellular processes during embryonic development and maintain homeostasis of adult tissues. A majority of Wnt signaling components are regulated by miRNAs which are small noncoding RNAs that are expressed in both animals and plants. In animal cells, miRNAs fine tune gene expression by pairing primarily to the 3'untranslated region of protein coding mRNAs to repress target mRNA translation and/or induce target degradation. miRNA-mediated regulation of signaling transduction pathways is important in modulating dose-sensitive response of cells to signaling molecules. This review discusses components of the Wnt signaling pathways that are regulated by miRNAs in the context of development and diseases. A fundamental understanding of miRNA functions in Wnt signaling transduction pathways may yield new insight into crosstalks of regulatory mechanisms essential for development and disease pathophysiology leading to novel therapeutics.

Submandibular parasympathetic gangliogenesis requires sprouty-dependent Wnt signals from epithelial progenitors

Parasympathetic innervation is critical for submandibular gland (SMG) development and regeneration. Parasympathetic ganglia (PSG) are derived from Schwann cell precursors that migrate along nerves, differentiate into neurons, and coalesce within their target tissue to form ganglia. However, signals that initiate gangliogenesis after the precursors differentiate into neurons are unknown. We found that deleting negative regulators of FGF signaling, Sprouty1 and Sprouty2 (Spry1/2DKO), resulted in a striking loss of gangliogenesis, innervation, and keratin 5-positive (K5+) epithelial progenitors in the SMG. Here we identify Wnts produced by K5+ progenitors in the SMG as key mediators of gangliogenesis. Wnt signaling increases survival and proliferation of PSG neurons, and inhibiting Wnt signaling disrupts gangliogenesis and organ innervation. Activating Wnt signaling and reducing FGF gene dosage rescues gangliogenesis and innervation in both the Spry1/2DKO SMG and pancreas. Thus, K5+ progenitors produce Wnt signals to establish the PSG-epithelial communication required for organ innervation and progenitor cell maintenance.

Lgr5 Marks Post-Mitotic, Lineage Restricted Cerebellar Granule Neurons during Postnatal Development

Wnt signaling regulates self-renewal and fate commitment of stem and progenitor cells in development and homeostasis. Leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5) is a co-receptor for Wnt signaling that marks highly proliferative stem and progenitor cells in many epithelial tissue types. Wnt signaling instructs neural developmental and homeostatic processes; however, Lgr5 expression in the developing and adult brain has not been characterized. Here we report that Lgr5 is expressed in the postnatal cerebellum during the maturation and synaptogenesis of cerebellar granule neurons (CGNs), processes controlled by Wnt signaling. Using a transgenic reporter mouse for in vivo Lgr5 expression analysis and lineage tracing, we reveal that Lgr5 specifically identified CGNs and was restricted temporally to the CGN maturation phase within the internal granule layer, but absent in the adult brain. Cells marked by Lgr5 were lineage restricted, post-mitotic and long-lived. The ligand for Lgr5, R-spondin, was secreted in a paracrine fashion that evolved during the maturation of CGNs, which coincided with the Lgr5 expression pattern. Our findings provide potential new insight into the critical regulation of Wnt signaling in the developing cerebellum and support a novel role for Lgr5 in the regulation of post-mitotic cells.

Inhibitory Effects of Bisphenol-A on Neural Stem Cells Proliferation and Differentiation in the Rat Brain Are Dependent on Wnt/β-Catenin Pathway

Neurogenesis, a process of generation of new neurons, occurs throughout the life in the hippocampus and sub-ventricular zone (SVZ). Bisphenol-A (BPA), an endocrine disrupter used as surface coating for packaged food cans, injures the developing and adult brain. However, the effects of BPA on neurogenesis and underlying cellular and molecular mechanism(s) are still unknown. Herein, we studied the effect(s) of prenatal and early postnatal exposure of low dose BPA on Wnt/β-catenin signaling pathway that controls different steps of neurogenesis such as neural stem cell (NSC) proliferation and neuronal differentiation. Pregnant rats were treated with 4, 40, and 400 μg BPA/kg body weight orally daily from gestational day 6 to postnatal day 21. Both in vivo and in vitro studies showed that BPA alters NSC proliferation and differentiation. BPA impaired NSC proliferation (5'-bromo-2'-deoxyuridine (BrdU(+)) and nestin(+) cells) and neuronal differentiation (BrdU/doublecortin(+) and BrdU/neuronal nuclei (NeuN(+)) cells) in the hippocampus and SVZ as compared to control. It significantly altered expression/protein levels of neurogenic genes and the Wnt pathway genes in the hippocampus. BPA reduced cellular β-catenin and p-GSK-3β levels and decreased β-catenin nuclear translocation, and cyclin-D1 and TCF/LEF promoter luciferase activity. Specific activation and blockage of the Wnt pathway suggested involvement of this pathway in BPA-mediated inhibition of neurogenesis. Further, blockage of GSK-3β activity by SB415286 and GSK-3β small interfering RNA (siRNA) attenuated BPA-induced downregulation of neurogenesis. Overall, these results suggest significant inhibitory effects of BPA on NSC proliferation and differentiation in the rat via the Wnt/β-catenin signaling pathway.

The Neuromuscular Junction: Aging at the Crossroad between Nerves and Muscle

Aging is associated with a progressive loss of muscle mass and strength and a decline in neurophysiological functions. Age-related neuromuscular junction (NMJ) plays a key role in musculoskeletal impairment that occurs with aging. However, whether changes in the NMJ precede or follow the decline of muscle mass and strength remains unresolved. Many factors such as mitochondrial dysfunction, oxidative stress, inflammation, changes in the innervation of muscle fibers, and mechanical properties of the motor units probably perform an important role in NMJ degeneration and muscle mass and strength decline in late life. This review addresses the primary events that might lead to NMJ dysfunction with aging, including studies on biomarkers, signaling pathways, and animal models. Interventions such as caloric restriction and exercise may positively affect the NMJ through this mechanism and attenuate the age-related progressive impairment in motor function.

Curcumin increased the differentiation rate of neurons in neural stem cells via wnt signaling in vitro study

BACKGROUND

The objective of the present study was to clarify the relationship between the neuroprotective effects of curcumin and the classical wnt signaling pathway.

METHOD

Using Sprague-Dawley rats at a gestational age of 14.5 d, we isolated neural stem cells from the anterior two-thirds of the fetal rat brain. The neural stem cells were passaged three times using the half media replacement method and identified using cellular immunofluorescence. After passaging for three generations, we cultured cells in media without basic fibroblast growth factor and epidermal growth factor. Then we treated cells in five different ways, including a blank control group, a group treated with IWR1 (10 μmol/L), a group treated with curcumin (500 nmol/L), a group treated with IWR1 + curcumin, and a group treated with dimethyl sulfoxide (10 μmol/L). We then measured the protein and RNA expression levels for wnt3a and β-catenin using Western blotting and Reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Western-blotting: after the third generation of cells had been treated for 72 h, we observed that wnt3a and β-catenin expression was significantly increased in the group receiving 500 nmol/L curcumin but not in the other groups. Furthermore, cells in the IWR1-treated group showed decreased wnt3a and β-catenin expression, and wnt3a and β-catenin was also decreased in the IWR1 + 500 nmol/L curcumin group. No obvious change was observed in the dimethyl sulfoxide group.

RT-PCR

RT-PCR showed similar changes to those observed with the Western blotting experiments.

CONCLUSIONS

Our study suggests that curcumin can activate the wnt signaling pathway, which provides evidence that curcumin exhibits a neuroprotective effect through the classical wnt signaling pathway.

MiR-135b is a direct PAX6 target and specifies human neuroectoderm by inhibiting TGF-β/BMP signaling

Several transcription factors (TFs) have been implicated in neuroectoderm (NE) development, and recently, the TF PAX6 was shown to be critical for human NE specification. However, microRNA networks regulating human NE development have been poorly documented. We hypothesized that microRNAs activated by PAX6 should promote NE development. Using a genomics approach, we identified PAX6 binding sites and active enhancers genome-wide in an in vitro model of human NE development that was based on neural differentiation of human embryonic stem cells (hESC). PAX6 binding to active enhancers was found in the proximity of several microRNAs, including hsa-miR-135b. MiR-135b was activated during NE development, and ectopic expression of miR-135b in hESC promoted differentiation toward NE. MiR-135b promotes neural conversion by targeting components of the TGF-β and BMP signaling pathways, thereby inhibiting differentiation into alternate developmental lineages. Our results demonstrate a novel TF-miRNA module that is activated during human neuroectoderm development and promotes the irreversible fate specification of human pluripotent cells toward the neural lineage.

Wnt and lithium: a common destiny in the therapy of nervous system pathologies?

Wnt signaling is required for neurogenesis, the fate of neural progenitors, the formation of neuronal circuits during development, neuron positioning and polarization, axon and dendrite development and finally for synaptogenesis. This signaling pathway is also implicated in the generation and differentiation of glial cells. In this review, we describe the mechanisms of action of Wnt signaling pathways and their implication in the development and correct functioning of the nervous system. We also illustrate how a dysregulated Wnt pathway could lead to psychiatric, neurodegenerative and demyelinating pathologies. Lithium, used for the treatment of bipolar disease, inhibits GSK3β, a central enzyme of the Wnt/β-catenin pathway. Thus, lithium could, to some extent, mimic Wnt pathway. We highlight the possible dialogue between lithium therapy and modulation of Wnt pathway in the treatment of the diseases of the nervous system.

The many faces of neuroendocrine differentiation in prostate cancer progression

In normal prostate, neuroendocrine (NE) cells are rare and interspersed among the epithelium. These cells are believed to provide trophic signals to epithelial cell populations through the secretion of an abundance of neuropeptides that can diffuse to influence surrounding cells. In the setting of prostate cancer (PC), NE cells can also stimulate surrounding prostate adenocarcinoma cell growth, but in some cases adenocarcinoma cells themselves acquire NE characteristics. This epithelial plasticity is associated with decreased androgen receptor (AR) signaling and the accumulation of neuronal and stem cell characteristics. Transformation to an NE phenotype is one proposed mechanism of resistance to contemporary AR-targeted treatments, is associated with poor prognosis, and thought to represent up to 25% of lethal PCs. Importantly, the advent of high-throughput technologies has started to provide clues for understanding the complex molecular profiles of tumors exhibiting NE differentiation. Here, we discuss these recent advances, the multifaceted manner by which an NE-like state may arise during the different stages of disease progression, and the potential benefit of this knowledge for the management of patients with advanced PC.

Role of wnt signaling in the control of adult hippocampal functioning in health and disease: therapeutic implications

It is well recognized the role of the Wnt pathway in many developmental processes such as neuronal maturation, migration, neuronal connectivity and synaptic formation. Growing evidence is also demonstrating its function in the mature brain where is associated with modulation of axonal remodeling, dendrite outgrowth, synaptic activity, neurogenesis and behavioral plasticity. Proteins involved in Wnt signaling have been found expressed in the adult hippocampus suggesting that Wnt pathway plays a role in the hippocampal function through life. Indeed, Wnt ligands act locally to regulate neurogenesis, neuronal cell shape and pre- and postsynaptic assembly, events that are thought to underlie changes in synaptic function associated with long-term potentiation and with cognitive tasks such as learning and memory. Recent data have demonstrated the increased expression of the Wnt antagonist Dickkopf-1 (DKK1) in brains of Alzheimer´s disease (AD) patients suggesting that dysfunction of Wnt signaling could also contribute to AD pathology. We review here evidence of Wnt-associated molecules expression linked to physiological and pathological hippocampal functioning in the adult brain. The basic aspects of Wnt related mechanisms underlying hippocampal plasticity as well as evidence of how hippocampal dysfunction may rely on Wnt dysregulation is analyzed. This information would provide some clues about the possible therapeutic targets for developing treatments for neurodegenerative diseases associated with aberrant brain plasticity.

Evidence for involvement of Wnt signalling in body polarities, cell proliferation, and the neuro-sensory system in an adult ctenophore

Signalling through the Wnt family of secreted proteins originated in a common metazoan ancestor and greatly influenced the evolution of animal body plans. In bilaterians, Wnt signalling plays multiple fundamental roles during embryonic development and in adult tissues, notably in axial patterning, neural development and stem cell regulation. Studies in various cnidarian species have particularly highlighted the evolutionarily conserved role of the Wnt/β-catenin pathway in specification and patterning of the primary embryonic axis. However in another key non-bilaterian phylum, Ctenophora, Wnts are not involved in early establishment of the body axis during embryogenesis. We analysed the expression in the adult of the ctenophore Pleurobrachia pileus of 11 orthologues of Wnt signalling genes including all ctenophore Wnt ligands and Fz receptors and several members of the intracellular β-catenin pathway machinery. All genes are strongly expressed around the mouth margin at the oral pole, evoking the Wnt oral centre of cnidarians. This observation is consistent with primary axis polarisation by the Wnts being a universal metazoan feature, secondarily lost in ctenophores during early development but retained in the adult. In addition, local expression of Wnt signalling genes was seen in various anatomical structures of the body including in the locomotory comb rows, where their complex deployment suggests control by the Wnts of local comb polarity. Other important contexts of Wnt involvement which probably evolved before the ctenophore/cnidarian/bilaterian split include proliferating stem cells and progenitors irrespective of cell types, and developing as well as differentiated neuro-sensory structures.

Adenomatous polyposis coli (APC) membrane recruitment 3, a member of the APC membrane recruitment family of APC-binding proteins, is a positive regulator of Wnt-β-catenin signalling

The adenomatous polyposis coli (APC) membrane recruitment (Amer) family proteins Amer1/Wilms tumour gene on the X chromosome and Amer2 are binding partners of the APC tumour suppressor protein, and act as negative regulators in the Wnt signalling cascade. So far, nothing has been known about the third member of the family, Amer3. Here we show that Amer3 binds to the armadillo repeat domain of APC, similarly to Amer1 and Amer2. Amer3 also binds to the Wnt pathway regulator conductin/axin2. Furthermore, we identified Amer1 as binding partner of Amer3. Whereas Amer1 and Amer2 are linked to the plasma membrane by an N-terminal membrane localization domain, Amer3 lacks this domain. Amer3 localizes to the cytoplasm and nucleus of epithelial cells, and this is dependent on specific nuclear import and export sequences. Functionally, exogenous Amer3 enhances the expression of a β-catenin/T-cell factor-dependent reporter gene, and knockdown of endogenous Amer3 reduces Wnt target gene expression in colorectal cancer cells. Thus, Amer3 acts as an activator of Wnt signalling, in contrast to Amer1 and Amer2, which are inhibitors, suggesting a nonredundant role of Amer proteins in the regulation of this pathway. Our data, together with those of previous studies, provide a comprehensive picture of similarities and differences within the Amer protein family.

Gene expression data reveal common pathways that characterize the unifocal nature of ovarian cancer

OBJECTIVE

The objective of the study was to evaluate the biological validity of ovarian cancer (OVCA) screening and early detection efforts and to characterize signaling pathways associated with human cancer metastasis and patient survival.

STUDY DESIGN

Using genome-wide expression profiling and deoxyribonucleic acid sequencing, we compared pelvic and matched extrapelvic implants from 30 patients with advanced-stage OVCA for expression of molecular signaling pathways and p53 gene mutations. Differentially expressed pathways were further evaluated in a series of primary or early-stage vs metastatic or recurrent cancer samples from 389 ovarian, prostate, and oral cancer patients. Metastasis pathways were also evaluated for associations with survival in 9 independent clinicogenomic datasets from 1691 ovarian, breast, colon, brain, and lung cancer and leukemia patients. The inhibitory effects of 1 pathway (transforming growth factor [TGF]-WNT) on in vitro OVCA cell migration were studied.

RESULTS

Pelvic and extrapelvic OVCA implants demonstrated similar patterns of signaling pathway expression and identical p53 mutations. However, we identified 3 molecular pathways/cellular processes that were differentially expressed between pelvic and extrapelvic OVCA samples and between primary/early-stage and metastatic/advanced or recurrent ovarian, oral, and prostate cancers. Furthermore, their expression was associated with overall survival from ovarian cancer (P = .006), colon cancer (1 pathway at P = .005), and leukemia (P = .05). Artesunate-induced TGF-WNT pathway inhibition impaired OVCA cell migration.

CONCLUSION

Advanced-stage OVCA has a unifocal origin in the pelvis. Molecular pathways associated with extrapelvic OVCA spread are also associated with metastasis from other human cancers and with overall patient survival. Such pathways represent appealing therapeutic targets for patients with metastatic disease.