Wnt-5a/Frizzled9 Receptor Signaling through the Gαo-Gβγ Complex Regulates Dendritic Spine Formation

Nobiletin regulates intracellular Ca2+ levels via IP3R and ameliorates neuroinflammation in Aβ42-induced astrocytes

Astrocytes are the major glial cells in the human brain and provide crucial metabolic and trophic support to neurons. The amyloid-β peptide (Aβ) alter the morphological and functional properties of astrocytes and induce inflammation and calcium dysregulation, contributing to Alzheimer's disease (AD) pathology. Recent studies highlight the role of Toll-like receptor (TLR) 4/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling in inflammation. Reactive oxygen species (ROS) generated due to Aβ, induce apoptosis in the brain cells worsening AD progression. Astrocytic cell surface receptors, such as purinergic receptors (P2Y1 and P2Y2), metabotropic glutamate receptor (mGLUR)5, α7 nicotinic acetylcholine receptor (α7nAChR), and N-methyl-d-aspartate receptors (NMDARs), have been suggested to interact with inositol trisphosphate receptor (IP3R) on the endoplasmic reticulum (ER) to induce Ca2+ movement from ER to cytoplasm, causing Ca2+ dysregulation. We found that the citrus flavonoid nobiletin (NOB) protected primary astrocytes from Aβ42-induced cytotoxicity and inhibited TLR4/NF-κB signaling in Aβ42-induced primary rat astrocytes. NOB was found to regulate Aβ42-induced ROS levels through Keap1-Nrf2 pathway. The receptors P2Y1, P2Y2, mGLUR5, α7nAChR, and NMDARs induced intracellular Ca2+ levels by activating IP3R and NOB regulated them, thereby regulating intracellular Ca2+ levels. Molecular docking analysis revealed a possible interaction between NOB and IP3R in IP3R regulation. Furthermore, RNA sequencing revealed various NOB-mediated biological signaling pathways, such as the AD-presenilin, AD-amyloid secretase, and Wnt signaling pathway, suggesting possible neuroprotective roles of NOB. To conclude, NOB is a promising therapeutic agent for AD and works by modulating AD pathology at various levels in Aβ42-induced primary rat astrocytes.

S-acylation of the Wnt receptor Frizzled-5 by zDHHC5 controls its cellular localization and synaptogenic activity in the rodent hippocampus

Proper localization of receptors for synaptic organizing factors is crucial for synapse formation. Wnt proteins promote synapse assembly through Frizzled (Fz) receptors. In hippocampal neurons, the surface and synaptic localization of Fz5 is regulated by neuronal activity, but the mechanisms involved remain poorly understood. Here, we report that all Fz receptors can be post-translationally modified by S-acylation and that Fz5 is S-acylated on three C-terminal cysteines by zDHHC5. S-acylation is essential for Fz5 localization to the cell surface, axons, and presynaptic sites. Notably, S-acylation-deficient Fz5 is internalized faster, affecting its association with signalosome components at the cell surface. S-acylation-deficient Fz5 also fails to activate canonical and divergent canonical Wnt pathways. Fz5 S-acylation levels are regulated by the pattern of neuronal activity. In vivo studies demonstrate that S-acylation-deficient Fz5 expression fails to induce presynaptic assembly. Our studies show that S-acylation of Frizzled receptors is a mechanism controlling their localization and function.

Frizzled 6 mutation regulates reserpine-induced depression-like behavior and Wnt signaling pathway in mice

BACKGROUND

Frizzled 6 (Fzd6) is involved in the development of various disorders; however, its role in the etiology of depression remains unclear. We aimed to determine the potential regulatory mechanisms of Fzd6 as a Wnt receptor in depression.

METHODS

Mice were divided into four groups: wild-type control (Fzd6WT-control), Fzd6 mutant control (Fzd6Q152E-control), wild-type reserpine (Fzd6WT-reserpine), and Fzd6 mutant reserpine (Fzd6Q152E-reserpine). Reserpine (0.5 mg/kg) was injected intraperitoneally for 10 days. Four behavioral experiments were performed to assess the effects of Fzd6Q152E on depression-like behaviors in the reserpine-treated mice. Blood samples were collected for an enzyme-linked immunosorbent assay (ELISA). Gene expression in the hippocampus was quantified using quantitative real-time polymerase chain reaction (qRT-PCR), and protein expression levels in the hippocampus were identified using western blotting.

RESULTS

The Fzd6 mutation affected reserpine-induced depression-like behavioral changes in mice. ELISA revealed significantly reduced serum levels of 5-hydroxytryptamine (5-HT), brain-derived neurotrophic factor (BDNF), and norepinephrine in both Fzd6Q152E-reserpine and Fzd6WT-reserpine mice, with a more pronounced decrease in Fzd6Q152E-reserpine mice, especially in norepinephrine expression. The qRT-PCR results showed significantly decreased Fzd6 expression in Fzd6Q152E-reserpine mice and altered expression of Dkk2, Gsk-3β, Lrp6, Wnt2, Wnt3, and Wnt3a in the Wnt pathway. Western blotting revealed decreased Fzd6 protein expression in Fzd6Q152E-control mice compared to Fzd6WT-control mice, whereas Fzd6 protein expression was restored in Fzd6Q152E-reserpine mice, and Gsk-3β expression was significantly changed.

CONCLUSION

Fzd6 potentially influences reserpine-induced depressive behavioral changes and serum depressive factor alterations and modulates the expression of the Wnt signaling pathway in the hippocampus of depressed mice.

Pathway selectivity in Frizzleds is achieved by conserved micro-switches defining pathway-determining, active conformations

The class Frizzled of G protein-coupled receptors (GPCRs), consisting of ten Frizzled (FZD1-10) paralogs and Smoothened, remains one of the most enigmatic GPCR families. This class mediates signaling predominantly through Disheveled (DVL) or heterotrimeric G proteins. However, the mechanisms underlying pathway selection are elusive. Here we employ a structure-driven mutagenesis approach in combination with an extensive panel of functional signaling readouts to investigate the importance of conserved state-stabilizing residues in FZD5 for signal specification. Similar data were obtained for FZD4 and FZD10 suggesting that our findings can be extrapolated to other members of the FZD family. Comparative molecular dynamics simulations of wild type and selected FZD5 mutants further support the concept that distinct conformational changes in FZDs specify the signal outcome. In conclusion, we find that FZD5 and FZDs in general prefer coupling to DVL rather than heterotrimeric G proteins and that distinct active state micro-switches in the receptor are essential for pathway selection arguing for conformational changes in the receptor protein defining transducer selectivity.

Microglial WNT5A supports dendritic spines maturation and neuronal firing

There is increasing evidence showing that microglia play a critical role in mediating synapse formation and spine growth, although the molecular mechanism remains elusive. Here, we demonstrate that the secreted morphogen WNT family member 5A (WNT5A) is the most abundant WNT expressed in microglia and that it promotes neuronal maturation. Co-culture of microglia with Thy1-YFP+ differentiated neurons significantly increased neuronal spine density and reduced dendritic spine turnover rate, which was diminished by silencing microglial Wnt5a in vitro. Co-cultured microglia increased post-synaptic marker PSD95 and synaptic density as determined by the co-localization of PSD95 with pre-synaptic marker VGLUT2 in vitro. The silencing of Wnt5a expression in microglia partially reduced both PSD95 and synaptic densities. Co-culture of differentiated neurons with microglia significantly enhanced neuronal firing rate as measured by multiple electrode array, which was significantly reduced by silencing microglial Wnt5a at 23 days differentiation in vitro. These findings demonstrate that microglia can mediate spine maturation and regulate neuronal excitability via WNT5A secretion indicating possible pathological roles of dysfunctional microglia in developmental disorders.

How Are Synapses Born? A Functional and Molecular View of the Role of the Wnt Signaling Pathway

Synaptic transmission is a dynamic process that requires precise regulation. Early in life, we must be able to forge appropriate connections (add and remove) to control our behavior. Neurons must recognize appropriate targets, and external soluble factors that activate specific signaling cascades provide the regulation needed to achieve this goal. Wnt signaling has been implicated in several forms of synaptic plasticity, including functional and structural changes associated with brain development. The analysis of synapses from an electrophysiological perspective allows us to characterize the functional role of cellular signaling pathways involved in brain development. The application of quantal theory to principles of developmental plasticity offers the possibility of dissecting the function of structural changes associated with the birth of new synapses as well as the maturation of immature silent synapses. Here, we focus on electrophysiological and molecular evidence that the Wnt signaling pathway regulates glutamatergic synaptic transmission, specifically N-methyl-d-aspartate receptors (NMDARs), to control the birth of new synapses. We also focus on the role of Wnts in the conversion of silent synapses into functional synapses.

The rearing environment persistently modulates mouse phenotypes from the molecular to the behavioural level

The phenotype of an organism results from its genotype and the influence of the environment throughout development. Even when using animals of the same genotype, independent studies may test animals of different phenotypes, resulting in poor replicability due to genotype-by-environment interactions. Thus, genetically defined strains of mice may respond differently to experimental treatments depending on their rearing environment. However, the extent of such phenotypic plasticity and its implications for the replicability of research findings have remained unknown. Here, we examined the extent to which common environmental differences between animal facilities modulate the phenotype of genetically homogeneous (inbred) mice. We conducted a comprehensive multicentre study, whereby inbred C57BL/6J mice from a single breeding cohort were allocated to and reared in 5 different animal facilities throughout early life and adolescence, before being transported to a single test laboratory. We found persistent effects of the rearing facility on the composition and heterogeneity of the gut microbial community. These effects were paralleled by persistent differences in body weight and in the behavioural phenotype of the mice. Furthermore, we show that environmental variation among animal facilities is strong enough to influence epigenetic patterns in neurons at the level of chromatin organisation. We detected changes in chromatin organisation in the regulatory regions of genes involved in nucleosome assembly, neuronal differentiation, synaptic plasticity, and regulation of behaviour. Our findings demonstrate that common environmental differences between animal facilities may produce facility-specific phenotypes, from the molecular to the behavioural level. Furthermore, they highlight an important limitation of inferences from single-laboratory studies and thus argue that study designs should take environmental background into account to increase the robustness and replicability of findings.

The phenotype of an organism results not only from its genotype but also the influence of its environment throughout development. This study shows that common environmental differences between animal facilities can induce substantial variation in the phenotype of mice, thereby highlighting an important limitation of inferences from single-laboratory studies in animal research.

Atypical deletion of Williams-Beuren syndrome reveals the mechanism of neurodevelopmental disorders

Genes associated with specific neurocognitive phenotypes in Williams–Beuren syndrome are still controversially discussed. This study identified nine patients with atypical deletions out of 111 patients with Williams–Beuren syndrome; these deletions included seven smaller deletions and two larger deletions. One patient had normal neurodevelopment with a deletion of genes on the distal side of the Williams–Beuren syndrome chromosomal region, including GTF2I and GTF2IRD1. However, another patient retained these genes but showed neurodevelopmental abnormalities. By comparing the genotypes and phenotypes of patients with typical and atypical deletions and previous reports in the literature, we hypothesize that the BAZ1B, FZD9, and STX1A genes may play an important role in the neurodevelopment of patients with WBS.

Epigenetic repression of Wnt receptors in AD: a role for Sirtuin2-induced H4K16ac deacetylation of Frizzled1 and Frizzled7 promoters

Growing evidence supports a role for deficient Wnt signalling in Alzheimer's disease (AD). First, the Wnt antagonist DKK1 is elevated in AD brains and is required for amyloid-β-induced synapse loss. Second, LRP6 Wnt co-receptor is required for synapse integrity and three variants of this receptor are linked to late-onset AD. However, the expression/role of other Wnt signalling components remain poorly explored in AD. Wnt receptors Frizzled1 (Fzd1), Fzd5, Fzd7 and Fzd9 are of interest due to their role in synapse formation/plasticity. Our analyses showed reduced FZD1 and FZD7 mRNA levels in the hippocampus of human early AD stages and in the hAPP^NLGF/NLGF mouse model. This transcriptional downregulation was accompanied by reduced levels of the pro-transcriptional histone mark H4K16ac and a concomitant increase of its deacetylase Sirt2 at Fzd1 and Fzd7 promoters in AD. In vitro and in vivo inhibition of Sirt2 rescued Fzd1 and Fzd7 mRNA expression and H4K16ac levels at their promoters. In addition, we showed that Sirt2 recruitment to Fzd1 and Fzd7 promoters is dependent on FoxO1 activity in AD, thus acting as a co-repressor. Finally, we found reduced levels of SIRT2 inhibitory phosphorylation in nuclear samples from human early AD stages with a concomitant increase in the SIRT2 phosphatase PP2C. This results in hyperactive nuclear Sirt2 and favours Fzd1 and Fzd7 repression in AD. Collectively, our findings define a novel role for nuclear hyperactivated SIRT2 in repressing Fzd1 and Fzd7 expression via H4K16ac deacetylation in AD. We propose SIRT2 as an attractive target to ameliorate AD pathology.

Local Wnt signalling in the asymmetric migrating vertebrate cells

Wnt signalling is known to generate cellular asymmetry via Wnt/planar cell polarity pathway (Wnt/PCP). Wnt/PCP acts locally (i) to orient membrane polarity and asymmetric establishment of intercellular junctions via conserved set of PCP proteins most specifically represented by Vangl and Prickle, and (ii) to asymmetrically rearrange cytoskeletal structures via downstream effectors of Dishevelled (Dvl). This process is best described on stable phenotypes of epithelial cells. Here, however, we review the activity of Wnt signalling in migratory cells which experience the extensive rearrangements of cytoskeleton and consequently dynamic asymmetry, making the localised effects of Wnt signalling easier to distinguish. Firstly, we focused on migration of neuronal axons, which allows to study how the pre-existent cellular asymmetry can influence Wnt signalling outcome. Then, we reviewed the role of Wnt signalling in models of mesenchymal migration including neural crest, melanoma, and breast cancer cells. Last, we collected evidence for local Wnt signalling in amoeboid cells, especially lymphocytes. As the outcome of this review, we identify blank spots in our current understanding of this topic, propose models that synthesise the current observations and allow formulation of testable hypotheses for the future research.

A Role for Frizzled and Their Post-Translational Modifications in the Mammalian Central Nervous System

The Wnt pathway is a key signalling cascade that regulates the formation and function of neuronal circuits. The main receptors for Wnts are Frizzled (Fzd) that mediate diverse functions such as neurogenesis, axon guidance, dendritogenesis, synapse formation, and synaptic plasticity. These processes are crucial for the assembly of functional neuronal circuits required for diverse functions ranging from sensory and motor tasks to cognitive performance. Indeed, aberrant Wnt-Fzd signalling has been associated with synaptic defects during development and in neurodegenerative conditions such as Alzheimer's disease. New studies suggest that the localisation and stability of Fzd receptors play a crucial role in determining Wnt function. Post-translational modifications (PTMs) of Fzd are emerging as an important mechanism that regulates these Wnt receptors. However, only phosphorylation and glycosylation have been described to modulate Fzd function in the central nervous system (CNS). In this review, we discuss the function of Fzd in neuronal circuit connectivity and how PTMs contribute to their function. We also discuss other PTMs, not yet described in the CNS, and how they might modulate the function of Fzd in neuronal connectivity. PTMs could modulate Fzd function by affecting Fzd localisation and stability at the plasma membrane resulting in local effects of Wnt signalling, a feature particularly important in polarised cells such as neurons. Our review highlights the importance of further studies into the role of PTMs on Fzd receptors in the context of neuronal connectivity.

Wnt5a modulates dendritic spine dynamics through the regulation of Cofilin via small Rho GTPase activity in hippocampal neurons

Dendritic spines are small, actin-rich protrusions that act as the receiving sites of most excitatory inputs in the central nervous system. The remodeling of the synapse architecture is mediated by actin cytoskeleton dynamics, a process precisely regulated by the small Rho GTPase family. Wnt ligands exert their presynaptic and postsynaptic effects during formation and consolidation of the synaptic structure. Specifically, Wnt5a has been identified as an indispensable synaptogenic factor for the regulation and organization of the postsynaptic side; however, the molecular mechanisms through which Wnt5a induces morphological changes resulting from actin cytoskeleton dynamics within dendritic spines remain unclear. In this work, we employ primary rat hippocampal cultures and HT22 murine hippocampal neuronal cell models, molecular and pharmacological tools, and fluorescence microscopy (laser confocal and epifluorescence) to define the Wnt5a-induced molecular signaling involved in postsynaptic remodeling mediated via the regulation of the small Rho GTPase family. We report that Wnt5a differentially regulates the phosphorylation of Cofilin in neurons through both Ras-related C3 botulinum toxin substrate 1 and cell division cycle 42 depending on the subcellular compartment and the extracellular calcium levels. Additionally, we demonstrate that Wnt5a increases the density of dendritic spines and promotes their maturation via Ras-related C3 botulinum toxin substrate 1. Accordingly, we find that Wnt5a requires the combined activation of small Rho GTPases to increase the levels of filamentous actin, thus promoting the stability of actin filaments. Altogether, these results provide evidence for a new mechanism by which Wnt5a may target actin dynamics, thereby regulating the subsequent morphological changes in dendritic spine architecture.

The transcriptional landscape of Alzheimer's disease and its association with Wnt signaling pathway

Alzheimer's disease (AD) is a neurological disorder primarily affecting the elderly. The disease manifests as progressive deterioration in cognitive functions, leading to a loss of autonomy. The identification of transcriptional changes in susceptible signaling pathways has provided clues to the origin and progression of AD and has pinpointed synapse loss as the prominent event in early stages of the disease. Synapse failure represents a key pathological correlate of cognitive decline in patients. Genetics and transcriptomics studies have also identified novel genes, processes, and pathways associated with AD. This evidence suggests that a deficiency in Wnt signaling pathway contributes to AD pathogenesis by inducing synaptic dysfunction and neuronal degeneration. In the adult nervous system, Wnt signaling plays a crucial role in synaptic physiology, modulating the synaptic vesicle cycle, trafficking neurotransmitter receptors, and modulating the expression of different genes associated with these processes. In this review, we describe the general transcriptional landscape associated with AD, specifically transcriptional changes associated with the Wnt signaling pathway and their effects in the context of disease.

Wnt-Frizzled Signaling Regulates Activity-Mediated Synapse Formation

The formation of synapses is a tightly regulated process that requires the coordinated assembly of the presynaptic and postsynaptic sides. Defects in synaptogenesis during development or in the adult can lead to neurodevelopmental disorders, neurological disorders, and neurodegenerative diseases. In order to develop therapeutic approaches for these neurological conditions, we must first understand the molecular mechanisms that regulate synapse formation. The Wnt family of secreted glycoproteins are key regulators of synapse formation in different model systems from invertebrates to mammals. In this review, we will discuss the role of Wnt signaling in the formation of excitatory synapses in the mammalian brain by focusing on Wnt7a and Wnt5a, two Wnt ligands that play an in vivo role in this process. We will also discuss how changes in neuronal activity modulate the expression and/or release of Wnts, resulting in changes in the localization of surface levels of Frizzled, key Wnt receptors, at the synapse. Thus, changes in neuronal activity influence the magnitude of Wnt signaling, which in turn contributes to activity-mediated synapse formation.

Ehrlichia chaffeensis TRP120 Is a Wnt Ligand Mimetic That Interacts with Wnt Receptors and Contains a Novel Repetitive Short Linear Motif That Activates Wnt Signaling

Ehrlichia chaffeensis expresses the TRP120 multifunctional effector, which is known to play a role in phagocytic entry, on the surface of infectious dense-cored ehrlichiae, but a cognate host receptor has not been identified. We recently reported that E. chaffeensis activates canonical Wnt signaling in monocytes to promote bacterial uptake and intracellular survival and that TRP120 was involved in this activation event. To identify the specific mechanism of pathway activation, we hypothesized that TRP120 is a Wnt signaling ligand mimetic that initiates Wnt pathway activity through direct interaction with the Wnt pathway Frizzled family of receptors. In this study, we used confocal immunofluorescence microscopy to demonstrate very strong colocalization between E. chaffeensis and Fzd2, 4, 5, 7, and 9 as well as coreceptor LRP5 at 1 to 3 h postinfection. Direct binding between TRP120 and multiple Fzd receptors was further confirmed by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR). Interfering RNA knockdown of Wnt receptors, coreceptors, and signaling pathway components significantly reduced E. chaffeensis infection, demonstrating that complex and redundant interactions are involved in Wnt pathway exploitation. We utilized in silico approaches to identify a repetitive short linear motif (SLiM) in TRP120 that is homologous to Wnt ligands and used mutant SLiM peptides and an α-TRP120-Wnt-SLiM antibody to demonstrate that the TRP120 Wnt SLiM activates the canonical Wnt pathway and promotes E. chaffeensis infection. This study reports the first example of bacterial mimicry of Wnt pathway ligands and highlights a pathogenic mechanism with potential for targeting by antimicrobial therapeutics.IMPORTANCE Upon infecting mammalian hosts, Ehrlichia chaffeensis establishes a replicative niche in microbe-eating immune system cells where it expertly orchestrates infection and spread. One of the ways Ehrlichia survives within these phagocytes is by activating evolutionarily conserved signaling pathways including the Wnt pathway; however, the molecular details of pathway hijacking have not been defined. This study is significant because it identifies an ehrlichial protein that directly interacts with components of the Wnt receptor complex, influencing pathway activity and promoting infection. Consequentially, Ehrlichia serves as a unique tool to investigate the intricacies of how pathogens repurpose human immune cell signaling and provides an opportunity to better understand many cellular processes in health and disease. Furthermore, understanding how this bacterium utilizes its small genome to survive within cells that evolved to destroy pathogens will facilitate the development of antibacterial therapeutics that could target Ehrlichia as well as other intracellular agents of human disease.

Wnt5a promotes hippocampal postsynaptic development and GluN2B-induced expression via the eIF2α HRI kinase

Wnt signaling plays a key role in neurodevelopment and neuronal maturation. Specifically, Wnt5a stimulates postsynaptic assemblies, increases glutamatergic neurotransmission and, through calcium signaling, generates nitric oxide (NO). Trying to unveil the molecular pathway triggering these postsynaptic effects, we found that Wnt5a treatment induces a time-dependent increases in the length of the postsynaptic density (PSD), elicits novel synaptic contacts and facilitates F-actin flow both in in vitro and ex vivo models. These effects were partially abolished by the inhibition of the Heme-regulated eukaryotic initiation factor 2α (HRI) kinase, a kinase which phosphorylates the initiation translational factor eIF2α. When phosphorylated, eIF2α normally avoids the translation of proteins not needed during stress conditions, in order to avoid unnecessary energetic expenses. However, phosphorylated eIF2α promotes the translation of some proteins with more than one open reading frame in its 5′ untranslated region. One of these proteins targeted by Wnt-HRI-eIF2α mediated translation is the GluN2B subunit of the NMDA receptor. The identified increase in GluN2B expression correlated with increased NMDA receptor function. Considering that NMDA receptors are crucial for excitatory synaptic transmission, the molecular pathway described here contributes to the understanding of the fast and plastic translational mechanisms activated during learning and memory processes.

Core transcriptional networks in Williams syndrome: IGF1-PI3K-AKT-mTOR, MAPK and actin signaling at the synapse echo autism

Gene networks for disorders of social behavior provide the mechanisms critical for identifying therapeutic targets and biomarkers. Large behavioral phenotypic effects of small human deletions make the positive sociality of Williams syndrome (WS) ideal for determining transcriptional networks for social dysfunction currently based on DNA variations for disorders such as autistic spectrum disorder (ASD) and schizophrenia (SCHZ). Consensus on WS networks has been elusive due to the need for larger cohort size, sensitive genome-wide detection and analytic tools. We report a core set of WS network perturbations in a cohort of 58 individuals (34 with typical, 6 atypical deletions and 18 controls). Genome-wide exon-level expression arrays robustly detected changes in differentially expressed gene (DEG) transcripts from WS deleted genes that ranked in the top 11 of 12 122 transcripts, validated by quantitative reverse transcription PCR, RNASeq and western blots. WS DEG's were strictly dosed in the full but not the atypical deletions that revealed a breakpoint position effect on non-deleted CLIP2, a caveat for current phenotypic mapping based on copy number variants. Network analyses tested the top WS DEG's role in the dendritic spine, employing GeneMANIA to harmonize WS DEGs with comparable query gene-sets. The results indicate perturbed actin cytoskeletal signaling analogous to the excitatory dendritic spines. Independent protein-protein interaction analyses of top WS DEGs generated a 100-node graph annotated topologically revealing three interacting pathways, MAPK, IGF1-PI3K-AKT-mTOR/insulin and actin signaling at the synapse. The results indicate striking similarity of WS transcriptional networks to genome-wide association study-based ASD and SCHZ risk suggesting common network dysfunction for these disorders of divergent sociality.

WNT Signaling Is a Key Player in Alzheimer's Disease

The cellular processes regulated by WNT signaling have been mainly studied during embryonic development and cancer. In the last two decades, the role of WNT in the adult central nervous system has been the focus of interest in our laboratory. In this chapter, we will be summarized β-catenin-dependent and -independent WNT pathways, then we will be revised WNT signaling function at the pre- and post-synaptic level. Concerning Alzheimer's disease (AD) initially, we found that WNT/β-catenin signaling activation exerts a neuroprotective mechanism against the amyloid β (Αβ) peptide toxicity. Later, we found that WNT/β-catenin participates in Tau phosphorylation and in learning and memory. In the last years, we demonstrated that WNT/β-catenin signaling is instrumental in the amyloid precursor protein (APP) processing and that WNT/β-catenin dysfunction results in Aβ production and aggregation. We highlight the importance of WNT/β-catenin signaling dysfunction in the onset of AD and propose that the loss of WNT/β-catenin signaling is a triggering factor of AD. The WNT pathway is therefore positioned as a therapeutic target for AD and could be a valid concept for improving AD therapy. We think that metabolism and inflammation will be relevant when defining future research in the context of WNT signaling and the neurodegeneration associated with AD.

Dysregulated Wnt Signalling in the Alzheimer's Brain

The Wnt signalling system is essential for both the developing and adult central nervous system. It regulates numerous cellular functions ranging from neurogenesis to blood brain barrier biology. Dysregulated Wnt signalling can thus have significant consequences for normal brain function, which is becoming increasingly clear in Alzheimer's disease (AD), an age-related neurodegenerative disorder that is the most prevalent form of dementia. AD exhibits a range of pathophysiological manifestations including aberrant amyloid precursor protein processing, tau pathology, synapse loss, neuroinflammation and blood brain barrier breakdown, which have been associated to a greater or lesser degree with abnormal Wnt signalling. Here we provide a comprehensive overview of the role of Wnt signalling in the CNS, and the research that implicates dysregulated Wnt signalling in the ageing brain and in AD pathogenesis. We also discuss the opportunities for therapeutic intervention in AD via modulation of the Wnt signalling pathway, and highlight some of the challenges and the gaps in our current understanding that need to be met to enable that goal.

Autism and Williams syndrome: Dissimilar socio-cognitive profiles with similar patterns of abnormal gene expression in the blood

LAY ABSTRACT

Autism spectrum disorders and Williams syndrome are complex cognitive conditions exhibiting quite opposite features in the social domain: whereas people with autism spectrum disorders are mostly hyposocial, subjects with Williams syndrome are usually reported as hypersocial. At the same time, autism spectrum disorders and Williams syndrome share some common underlying behavioral and cognitive deficits. It is not clear, however, which genes account for the attested differences (and similarities) in the socio-cognitive domain. In this article, we adopted a comparative molecular approach and looked for genes that might be differentially (or similarly) regulated in the blood of people with these conditions. We found a significant overlap between genes dysregulated in the blood of patients compared to neurotypical controls, with most of them being upregulated or, in some cases, downregulated. Still, genes with similar expression trends can exhibit quantitative differences between conditions, with most of them being more dysregulated in Williams syndrome than in autism spectrum disorders. Differentially expressed genes are involved in aspects of brain development and function (particularly dendritogenesis) and are expressed in brain areas (particularly the cerebellum, the thalamus, and the striatum) of relevance for the autism spectrum disorder and the Williams syndrome etiopathogenesis. Overall, these genes emerge as promising candidates for the similarities and differences between the autism spectrum disorder and the Williams syndrome socio-cognitive profiles.

Frizzled Receptors in Tumors, Focusing on Signaling, Roles, Modulation Mechanisms, and Targeted Therapies

Wnt molecules play crucial roles in development and adult homeostasis through their receptors Frizzled proteins (Fzds). Fzds mediate canonical β-catenin pathway and various noncanonical β-catenin-independent pathways. Aberrant Fzd signaling is involved in many diseases including cancer. Wnt/β-catenin is a well-established oncogenic pathway involved in almost every aspect of tumor development. However, Fzd-mediated noncanonical Wnt pathways function as both tumor promoters and tumor suppressors depending on cellular context. Fzd-targeted therapies have proven to be effective on cultured tumor cells, tumor cell xenografts, mouse tumor models, and patient-derived xenografts (PDX). Moreover, Fzd-targeted therapies synergize with chemotherapy in preclinical models. However, the occurrence of fragility fractures in patients treated with Fzd-targeted agents such as OMP-54F28 and OMP-18R5 limits the development of this combination. Along with new insights on signaling, roles, and modulation mechanisms of Fzds in human tumors, more Fzd-related therapeutic targets will be developed.

Cell-surface markers identify tissue resident multipotential stem/stromal cell subsets in synovial intimal and sub-intimal compartments with distinct chondrogenic properties

OBJECTIVE

Synovium contains multipotent progenitor/stromal cells (MPCs) with potential to participate in cartilage repair. Understanding the identity of these MPCs will allow their therapeutic potential to be fully exploited. Hence this study aimed to identify primary synovial MPCs and characterize them in the context of cartilage regeneration.

METHODS

Primary MPC/MPC-subset specific markers in synovium were identified by FACS analysis of uncultured cells. MPC-subsets from human synovium obtained from patients undergoing total knee arthroplasty were FACS sorted, cultured, immunophenotyped and chondrogenically differentiated. The anatomical localization of MPCs in synovium was examined using immunohistochemistry. Finally, the presence of these MPC subsets in healthy synovium obtained from human organ donors was examined.

RESULTS

A combination of CD45, CD31, CD73 and CD90 can isolate two distinct MPC-subsets in synovium. These MPC-subsets, freshly isolated from synovium, did not express CD45 or CD31, but expressed CD73. Additionally, a sub-population of CD73⁺ cells also expressed CD90. CD45^-CD31^-CD73⁺CD90^- cells were significantly more chondrogenic than CD45^-CD31^-CD73⁺CD90⁺ cells in the presence of TGFβ1. Interestingly, reduced chondrogenic ability of CD73⁺CD90⁺ cells could be reversed by the addition of BMP2, showing discrete chondrogenic factor requirements by distinct cell-subsets. In addition, these MPCs had distinct anatomical localization; CD73 was expressed both in intimal and sub-intimal region while CD90 was enriched in the sub-intimal region. We further demonstrated that these subsets are also present in healthy synovium.

CONCLUSIONS

We provide indications that primary MPCs in synovial intima and sub-intima are phenotypically and functionally distinct with different chondrogenic properties.

Wnt5a promotes differentiation and development of adult-born neurons in the hippocampus by noncanonical Wnt signaling

In the adult hippocampus, new neurons are generated in the dentate gyrus. The Wnt signaling pathway regulates this process, but little is known about the endogenous Wnt ligands involved. We investigated the role of Wnt5a on adult hippocampal neurogenesis. Wnt5a regulates neuronal morphogenesis during embryonic development, and maintains dendritic architecture of pyramidal neurons in the adult hippocampus. Here, we determined that Wnt5a knockdown in the mouse dentate gyrus by lentivirus-mediated shRNA impaired neuronal differentiation of progenitor cells, and reduced dendritic development of adult-born neurons. In cultured adult hippocampal progenitors (AHPs), Wnt5a knockdown reduced neuronal differentiation and morphological development of AHP-derived neurons, whereas treatment with Wnt5a had the opposite effect. Interestingly, no changes in astrocytic differentiation were observed in vivo or in vitro, suggesting that Wnt5a does not affect fate-commitment. By using specific inhibitors, we determined that Wnt5a signals through CaMKII to induce neurogenesis, and promotes dendritic development of newborn neurons through activating Wnt/JNK and Wnt/CaMKII signaling. Our results indicate Wnt5a as a niche factor in the adult hippocampus that promotes neuronal differentiation and development through activation of noncanonical Wnt signaling pathways.

Molecular Pharmacology of Class F Receptor Activation

The class Frizzled (FZD) or class F of G protein-coupled receptors consists of 10 FZD paralogues and Smoothened (SMO). FZDs coordinate wingless/Int-1 signaling and SMO mediates Hedgehog signaling. Class F receptor signaling is intrinsically important for embryonic development and its dysregulation leads to diseases, including diverse forms of tumors. With regard to the importance of class F signaling in human disease, these receptors provide an attractive target for therapeutics, exemplified by the use of SMO antagonists for the treatment of basal cell carcinoma. Here, we review recent structural insights in combination with a more detailed functional understanding of class F receptor activation, G protein coupling, conformation-based functional selectivity, and mechanistic details of activating cancer mutations, which will lay the basis for further development of class F-targeting small molecules for human therapy. SIGNIFICANCE STATEMENT: Stimulated by recent insights into the activation mechanisms of class F receptors from structural and functional analysis of Frizzled and Smoothened, we aim to summarize what we know about the molecular details of ligand binding, agonist-driven conformational changes, and class F receptor activation. A better understanding of receptor activation mechanisms will allow us to engage in structure- and mechanism-driven drug discovery with the potential to develop more isoform-selective and potentially pathway-selective drugs for human therapy.

Frizzled-9+ Supporting Cells Are Progenitors for the Generation of Hair Cells in the Postnatal Mouse Cochlea

Lgr5+ cochlear supporting cells (SCs) have been reported to be hair cell (HC) progenitor cells that have the ability to regenerate HCs in the neonatal mouse cochlea, and these cells are regulated by Wnt signaling. Frizzled-9 (Fzd9), one of the Wnt receptors, has been reported to be used to mark neuronal stem cells in the brain together with other markers and mesenchymal stem cells from human placenta and bone marrow. Here we used Fzd9-CreER mice to lineage label and trace Fzd9+ cells in the postnatal cochlea in order to investigate the progenitor characteristic of Fzd9+ cells. Lineage labeling showed that inner phalangeal cells (IPhCs), inner border cells (IBCs), and third-row Deiters’ cells (DCs) were Fzd9+ cells, but not inner pillar cells (IPCs) or greater epithelial ridge (GER) cells at postnatal day (P)3, which suggests that Fzd9+ cells are a much smaller cell population than Lgr5+ progenitors. The expression of Fzd9 progressively decreased and was too low to allow lineage tracing after P14. Lineage tracing for 6 days in vivo showed that Fzd9+ cells could also generate similar numbers of new HCs compared to Lgr5+ progenitors. A sphere-forming assay showed that Fzd9+ cells could form spheres after sorting by flow cytometry, and when we compared the isolated Fzd9+ cells and Lgr5+ progenitors there were no significant differences in sphere number or sphere diameter. In a differentiation assay, the same number of Fzd9+ cells could produce similar amounts of Myo7a+ cells compared to Lgr5+ progenitors after 10 days of differentiation. All these data suggest that the Fzd9+ cells have a similar capacity for proliferation, differentiation, and HC generation as Lgr5+ progenitors and that Fzd9 can be used as a more restricted marker of HC progenitors.

GALECTIN-8 Is a Neuroprotective Factor in the Brain that Can Be Neutralized by Human Autoantibodies

Galectin-8 (Gal-8) is a glycan-binding protein that modulates a variety of cellular processes interacting with cell surface glycoproteins. Neutralizing anti-Gal-8 antibodies that block Gal-8 functions have been described in autoimmune and inflammatory disorders, likely playing pathogenic roles. In the brain, Gal-8 is highly expressed in the choroid plexus and accordingly has been detected in human cerebrospinal fluid. It protects against central nervous system autoimmune damage through its immune-suppressive potential. Whether Gal-8 plays a direct role upon neurons remains unknown. Here, we show that Gal-8 protects hippocampal neurons in primary culture against damaging conditions such as nutrient deprivation, glutamate-induced excitotoxicity, hydrogen peroxide (H₂O₂)-induced oxidative stress, and β-amyloid oligomers (Aβo). This protective action is manifested even after 2 h of exposure to the harmful condition. Pull-down assays demonstrate binding of Gal-8 to selected β1-integrins, including α3 and α5β1. Furthermore, Gal-8 activates β1-integrins, ERK1/2, and PI3K/AKT signaling pathways that mediate neuroprotection. Hippocampal neurons in primary culture produce and secrete Gal-8, and their survival decreases upon incubation with human function-blocking Gal-8 autoantibodies obtained from lupus patients. Despite the low levels of Gal-8 expression detected by real-time PCR in hippocampus, compared with other brain regions, the complete lack of Gal-8 in Gal-8 KO mice determines higher levels of apoptosis upon H₂O₂ stereotaxic injection in this region. Therefore, endogenous Gal-8 likely contributes to generate a neuroprotective environment in the brain, which might be eventually counteracted by human function-blocking autoantibodies.

Structural insight into Class F receptors - What have we learnt regarding agonist-induced activation?

Class F receptors, including the ten Frizzleds (FZD_1-10 ) and SMO, mediate the effects of WNTs and hedgehog proteins and belong to the superfamily of G protein-coupled receptors (GPCRs). While the recent, high-resolution insight into mechanisms of GPCR activation provides a better understanding of receptor activation in Class A, B and C GPCRs, it remains unclear how Class F receptors bind their ligands, how ligand binding is translated to receptor activation and how signal initiation and specification are achieved. Here, we summarize recent efforts in elucidating Class F receptor structure and activation mechanisms and critically discuss the progress made in this area. A better understanding of the activation mechanisms of Class F receptors is required to engage in mechanism-based and structure-guided drug discovery to exploit the large therapeutic potential of targeting these receptors pharmacologically.

The cell type resolved mouse transcriptome in neuron-enriched brain tissues from the hippocampus and cerebellum during prion disease

Multiple cell types and complex connection networks are an intrinsic feature of brain tissue. In this study we used expression profiling of specific microscopic regions of heterogeneous tissue sections isolated by laser capture microdissection (LCM) to determine insights into the molecular basis of brain pathology in prion disease. Temporal profiles in two mouse models of prion disease, bovine spongiform encephalopathy (BSE) and a mouse-adapted strain of scrapie (RML) were performed in microdissected regions of the CA1 hippocampus and granular layer of the cerebellum which are both enriched in neuronal cell bodies. We noted that during clinical disease the number of activated microglia and astrocytes that occur in these areas are increased, thereby likely diluting the neuronal gene expression signature. We performed a comparative analysis with gene expression profiles determined from isolated populations of neurons, microglia and astrocytes to identify transcripts that are enriched in each of these cell types. Although the incubation periods of these two models are quite different, over 300 days for BSE and ~160 days for RML scrapie, these regional microdissections revealed broadly similar profiles. Microglial and astrocyte-enriched genes contributed a profound inflammatory profile consisting of inflammatory cytokines, genes related to phagocytosis, proteolysis and genes coding for extracellular matrix proteins. CA1 pyramidal neurons displayed a net upregulation of transcription factors and stress induced genes at pre-clinical stages of disease while all tissues showed profound decrease of overlapping genes related to neuronal function, in particular transcripts related to neuronal communication including glutamate receptors, phosphatase subunits and numerous synapse-related markers. Of note, we found a small number of genes expressed in neurons that were upregulated during clinical disease including, COX6A2, FZD9, RXRG and SOX11, that may be biomarkers of neurodegeneration.

FZD5 is a Gαq-coupled receptor that exhibits the functional hallmarks of prototypical GPCRs

Frizzleds (FZDs) are a group of seven transmembrane-spanning (7TM) receptors that belong to class F of the G protein-coupled receptor (GPCR) superfamily. FZDs bind WNT proteins to stimulate diverse signaling cascades involved in embryonic development, stem cell regulation, and adult tissue homeostasis. Frizzled 5 (FZD₅) is one of the most studied class F GPCRs that promote the functional inactivation of the β-catenin destruction complex in response to WNTs. However, whether FZDs function as prototypical GPCRs has been heavily debated and, in particular, FZD₅ has not been shown to activate heterotrimeric G proteins. Here, we show that FZD₅ exhibited a conformational change after the addition of WNT-5A, which is reminiscent of class A and class B GPCR activation. In addition, we performed several live-cell imaging and spectrometric-based approaches, such as dual-color fluorescence recovery after photobleaching (dcFRAP) and resonance energy transfer (RET)-based assays that demonstrated that FZD₅ activated Gα_q and its downstream effectors upon stimulation with WNT-5A. Together, these findings suggest that FZD₅ is a 7TM receptor with a bona fide GPCR activation profile and suggest novel targets for drug discovery in WNT-FZD signaling.

Wnt signalling in the development of axon, dendrites and synapses

Wnts are a highly conserved family of secreted glycoproteins that play essential roles in the morphogenesis and body patterning during the development of metazoan species. In recent years, mounting evidence has revealed important functions of Wnt signalling in diverse aspects of neural development, including neuronal polarization, guidance and branching of the axon and dendrites, as well as synapse formation and its structural remodelling. In contrast to Wnt signalling in cell proliferation and differentiation, which mostly acts through β-catenin-dependent pathways, Wnts engage a diverse array of non-transcriptional cascades in neuronal development, such as the planar cell polarity, cytoskeletal or calcium signalling pathways. In this review, we summarize recent advances in the mechanisms of Wnt signalling in the development of axon, dendrite and synapse formation.

Frizzleds as GPCRs - More Conventional Than We Thought!

For more than 30 years, WNT/β-catenin and planar cell polarity signaling has formed the basis for what we understand to be the primary output of the interaction between WNTs and their cognate receptors known as Frizzleds (FZDs). In the shadow of these pathways, evidence for the involvement of heterotrimeric G proteins in WNT signaling has grown substantially over the years - redefining the complexity of the WNT signaling network. Moreover, the distinct characteristics of FZD paralogs are becoming better understood, and we can now apply concepts valid for classical GPCRs to grasp FZDs as molecular machines at the interface of ligand binding and intracellular effects. This review discusses recent developments in the field of WNT/FZD signaling in the context of GPCR pharmacology, and identifies remaining mysteries with an emphasis on structural and kinetic components that support this dogma shift.

Wnt Signaling Mediates LTP-Dependent Spine Plasticity and AMPAR Localization through Frizzled-7 Receptors

The structural and functional plasticity of synapses is critical for learning and memory. Long-term potentiation (LTP) induction promotes spine growth and AMPAR accumulation at excitatory synapses, leading to increased synaptic strength. Glutamate initiates these processes, but the contribution from extracellular modulators is not fully established. Wnts are required for spine formation; however, their impact on activity-mediated spine plasticity and AMPAR localization is unknown. We found that LTP induction rapidly increased synaptic Wnt7a/b protein levels. Acute blockade of endogenous Wnts or loss of postsynaptic Frizzled-7 (Fz7) receptors impaired LTP-mediated synaptic strength, spine growth, and AMPAR localization at synapses. Live imaging of SEP-GluA1 and single-particle tracking revealed that Wnt7a rapidly promoted synaptic AMPAR recruitment and trapping. Wnt7a, through Fz7, induced CaMKII-dependent loss of SynGAP from spines and increased extrasynaptic AMPARs by PKA phosphorylation. We identify a critical role for Wnt-Fz7 signaling in LTP-mediated synaptic accumulation of AMPARs and spine plasticity.

Loss of canonical Wnt signaling is involved in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the older population, however, the precise cause of the disease is unknown. The neuropathology is characterized by the presence of aggregates formed by amyloid-β (Aβ) peptide and phosphorylated tau; which is accompanied by progressive impairment of memory. Diverse signaling pathways are linked to AD, and among these the Wnt signaling pathway is becoming increasingly relevant, since it plays essential roles in the adult brain. Initially, Wnt signaling activation was proposed as a neuroprotective mechanism against Aβ toxicity. Later, it was reported that it participates in tau phosphorylation and processes of learning and memory. Interestingly, in the last years we demonstrated that Wnt signaling is fundamental in amyloid precursor protein (APP) processing and that Wnt dysfunction results in Aβ production and aggregation in vitro. Recent in vivo studies reported that loss of canonical Wnt signaling exacerbates amyloid deposition in a transgenic (Tg) mouse model of AD. Finally, we showed that inhibition of Wnt signaling in a Tg mouse previously at the appearance of AD signs, resulted in memory loss, tau phosphorylation and Aβ formation and aggregation; indicating that Wnt dysfunction accelerated the onset of AD. More importantly, Wnt signaling loss promoted cognitive impairment, tau phosphorylation and Aβ_1-42 production in the hippocampus of wild-type (WT) mice, contributing to the development of an Alzheimer's-like neurophatology. Therefore, in this review we highlight the importance of Wnt/β-catenin signaling dysfunction in the onset of AD and propose that the loss of canonical Wnt signaling is a triggering factor of AD.

Wnt Signaling in the Central Nervous System: New Insights in Health and Disease

Since its discovery, Wnt signaling has been shown to be one of the most crucial morphogens in development and during the maturation of central nervous system. Its action is relevant during the establishment and maintenance of synaptic structure and neuronal function. In this chapter, we will discuss the most recent evidence on these aspects, and we will explore the evidence that involves Wnt signaling on other less known functions, such as in adult neurogenesis, in the generation of oscillatory neural rhythms, and in adult behavior. The dysfunction of Wnt signaling at different levels will be also discussed, in particular in those aspects that have been found to be linked with several neurodegenerative diseases and neurological disorders. Finally, we will address the possibility of Wnt signaling manipulation to treat those pathophysiological aspects.

APP/Go protein Gβγ-complex signaling mediates Aβ degeneration and cognitive impairment in Alzheimer's disease models

Deposition of amyloid-β (Aβ), the proteolytic product of the amyloid precursor protein (APP), might cause neurodegeneration and cognitive decline in Alzheimer's disease (AD). However, the direct involvement of APP in the mechanism of Aβ-induced degeneration in AD remains on debate. Here, we analyzed the interaction of APP with heterotrimeric Go protein in primary hippocampal cultures and found that Aβ deposition dramatically enhanced APP-Go protein interaction in dystrophic neurites. APP overexpression rendered neurons vulnerable to Aβ toxicity by a mechanism that required Go-Gβγ complex signaling and p38-mitogen-activated protein kinase activation. Gallein, a selective pharmacological inhibitor of Gβγ complex, inhibited Aβ-induced dendritic and axonal dystrophy, abnormal tau phosphorylation, synaptic loss, and neuronal cell death in hippocampal neurons expressing endogenous protein levels. In the 3xTg-AD mice, intrahippocampal application of gallein reversed memory impairment associated with early Aβ pathology. Our data provide further evidence for the involvement of APP/Go protein in Aβ-induced degeneration and reveal that Gβγ complex is a signaling target potentially relevant for developing therapies for halting Aβ degeneration in AD.

Role of G Protein-Coupled Receptors in the Regulation of Structural Plasticity and Cognitive Function

Cognition and other higher brain functions are known to be intricately associated with the capacity of neural circuits to undergo structural reorganization. Structural remodelling of neural circuits, or structural plasticity, in the hippocampus plays a major role in learning and memory. Dynamic modifications of neuronal connectivity in the form of dendritic spine morphology alteration, as well as synapse formation and elimination, often result in the strengthening or weakening of specific neural circuits that determine synaptic plasticity. Changes in dendritic complexity and synapse number are mediated by cellular processes that are regulated by extracellular signals such as neurotransmitters and neurotrophic factors. As many neurotransmitters act on G protein-coupled receptors (GPCRs), it has become increasingly apparent that GPCRs can regulate structural plasticity through a myriad of G protein-dependent pathways and non-canonical signals. A thorough understanding of how GPCRs exert their regulatory influence on dendritic spine morphogenesis may provide new insights for treating cognitive impairment and decline in various age-related diseases. In this article, we review the evidence of GPCR-mediated regulation of structural plasticity, with a special emphasis on the involvement of common as well as distinct signalling pathways that are regulated by major neurotransmitters.

High expression of G-protein signaling modulator 2 in hepatocellular carcinoma facilitates tumor growth and metastasis by activating the PI3K/AKT signaling pathway

The aim of this study was to investigate the role of G-protein signaling modulator 2 in the carcinogenesis and progression of hepatocellular carcinoma. We previously showed that G-protein signaling modulator 2 was upregulated in hepatitis B virus-related hepatocellular carcinoma tissues through a hierarchical clustering analysis. With this study, we first assessed the expression pattern of G-protein signaling modulator 2 in hepatocellular carcinoma specimens and adjacent noncancerous tissues; clinical data were analyzed, along survival times, utilizing the Kaplan-Meier method. Moreover, the functions of G-protein signaling modulator 2 were examined using small-interfering RNAs in vitro. The results showed that G-protein signaling modulator 2 was clearly overexpressed in hepatocellular carcinoma tissues and cell lines and that the G-protein signaling modulator 2 expression level was related to tumor size and hepatitis B virus infection. Furthermore, G-protein signaling modulator 2 knockdown studies suggested that G-protein signaling modulator 2 accelerates cell growth, cell cycle, migration, and invasion and inhibits apoptosis, acting as an oncogene in hepatocellular carcinoma. Western blotting indicated that silencing of G-protein signaling modulator 2 in HepG2 and SMMC-7721 cells increased the expression levels of Bax, caspase-3, and E-cadherin, while notably suppressing the cyclin-dependent kinase 4, cyclin-dependent kinase 6, CyclinD1, Snail1, Vimentin, and matrix metallopeptidase 9 expression levels, compared with that in the control groups. In addition, we found that G-protein signaling modulator 2 can affect the expression of key proteins involved in protein kinase B activation. In conclusion, high expression of G-protein signaling modulator 2 was involved in the pathological processes of hepatocellular carcinoma through activation of the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, which may provide an attractive potential diagnostic biomarker and therapeutic target for treatment of hepatocellular carcinoma.

FZD10-Gα13 signalling axis points to a role of FZD10 in CNS angiogenesis

Among the 10 Frizzled (FZD) isoforms belonging to the Class F of G protein-coupled receptors (GPCRs), FZD₁₀ remains the most enigmatic. FZD₁₀ shows homology to FZD₄ and FZD₉ and was previously implicated in both β-catenin-dependent and -independent signalling. In normal tissue, FZD₁₀ levels are generally very low; however, its upregulation in synovial carcinoma has attracted some attention for therapy. Our findings identify FZD₁₀ as a receptor interacting with and signalling through the heterotrimeric G protein Gα₁₃ but not Gα_12, Gα_i1, Gα_oA, Gα_s, or Gα_q. Stimulation with the FZD agonist WNT induced the dissociation of the Gα₁₃ protein from FZD₁₀, and led to global Gα_12/13-dependent cell changes assessed by dynamic mass redistribution measurements. Furthermore, we show that FZD₁₀ mediates Gα_12/13 activation-dependent induction of YAP/TAZ transcriptional activity. In addition, we show a distinct expression of FZD₁₀ in embryonic CNS endothelial cells at E11.5-E14.5. Given the well-known importance of Gα₁₃ signalling for the development of the vascular system, the selective expression of FZD₁₀ in brain vascular endothelial cells points at a potential role of FZD₁₀-Gα₁₃ signalling in CNS angiogenesis.

Wnt5a is essential for hippocampal dendritic maintenance and spatial learning and memory in adult mice

Stability of neuronal connectivity is critical for brain functions, and morphological perturbations are associated with neurodegenerative disorders. However, how neuronal morphology is maintained in the adult brain remains poorly understood. Here, we identify Wnt5a, a member of the Wnt family of secreted morphogens, as an essential factor in maintaining dendritic architecture in the adult hippocampus and for related cognitive functions in mice. Wnt5a expression in hippocampal neurons begins postnatally, and its deletion attenuated CaMKII and Rac1 activity, reduced GluN1 glutamate receptor expression, and impaired synaptic plasticity and spatial learning and memory in 3-mo-old mice. With increased age, Wnt5a loss caused progressive attrition of dendrite arbors and spines in Cornu Ammonis (CA)1 pyramidal neurons and exacerbated behavioral defects. Wnt5a functions cell-autonomously to maintain CA1 dendrites, and exogenous Wnt5a expression corrected structural anomalies even at late-adult stages. These findings reveal a maintenance factor in the adult brain, and highlight a trophic pathway that can be targeted to ameliorate dendrite loss in pathological conditions.

Activation of Wnt Signaling in Cortical Neurons Enhances Glucose Utilization through Glycolysis

The Wnt signaling pathway is critical for a number of functions in the central nervous system, including regulation of the synaptic cleft structure and neuroprotection against injury. Deregulation of Wnt signaling has been associated with several brain pathologies, including Alzheimer's disease. In recent years, it has been suggested that the Wnt pathway might act as a central integrator of metabolic signals from peripheral organs to the brain, which would represent a new role for Wnt signaling in cell metabolism. Energy metabolism is critical for normal neuronal function, which mainly depends on glucose utilization. Brain energy metabolism is important in almost all neurological disorders, to which a decrease in the capacity of the brain to utilize glucose has been linked. However, little is known about the relationship between Wnt signaling and neuronal glucose metabolism in the cellular context. In the present study, we found that acute treatment with the Wnt3a ligand induced a large increase in glucose uptake, without changes in the expression or localization of glucose transporter type 3. In addition, we observed that Wnt3a treatment increased the activation of the metabolic sensor Akt. Moreover, we observed an increase in the activity of hexokinase and in the glycolytic rate, and both processes were dependent on activation of the Akt pathway. Furthermore, we did not observe changes in the activity of glucose-6-phosphate dehydrogenase or in the pentose phosphate pathway. The effect of Wnt3a was independent of both the transcription of Wnt target genes and synaptic effects of Wnt3a. Together, our results suggest that Wnt signaling stimulates glucose utilization in cortical neurons through glycolysis to satisfy the high energy demand of these cells.