WASP-1, a canonical Wnt signaling potentiator, rescues hippocampal synaptic impairments induced by Aβ oligomers

Wnt/β-catenin Signaling in Central Nervous System Regeneration

The Wnt/β-catenin signaling pathway plays a pivotal role in the development, maintenance, and repair of the central nervous system (CNS). This chapter explores the diverse functions of Wnt/β-catenin signaling, from its critical involvement in embryonic CNS development to its reparative and plasticity-inducing roles in response to CNS injury. We discuss how Wnt/β-catenin signaling influences various CNS cell types-astrocytes, microglia, neurons, and oligodendrocytes-each contributing to repair and plasticity after injury. The chapter also addresses the pathway's involvement in CNS disorders such as Alzheimer's and Parkinson's diseases, psychiatric disorders, and traumatic brain injury (TBI), highlighting potential Wnt-based therapeutic approaches. Lastly, zebrafish are presented as a promising model organism for studying CNS regeneration and neurodegenerative diseases, offering insights into future research and therapeutic development.

WNT-β Catenin Signaling as a Potential Therapeutic Target for Neurodegenerative Diseases: Current Status and Future Perspective

Wnt/β-catenin (WβC) signaling pathway is an important signaling pathway for the maintenance of cellular homeostasis from the embryonic developmental stages to adulthood. The canonical pathway of WβC signaling is essential for neurogenesis, cell proliferation, and neurogenesis, whereas the noncanonical pathway (WNT/Ca²⁺ and WNT/PCP) is responsible for cell polarity, calcium maintenance, and cell migration. Abnormal regulation of WβC signaling is involved in the pathogenesis of several neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and spinal muscular atrophy (SMA). Hence, the alteration of WβC signaling is considered a potential therapeutic target for the treatment of neurodegenerative disease. In the present review, we have used the bibliographical information from PubMed, Google Scholar, and Scopus to address the current prospects of WβC signaling role in the abovementioned neurodegenerative diseases.

The Multifaceted Role of WNT Signaling in Alzheimer's Disease Onset and Age-Related Progression

The evolutionary conserved WNT signaling pathway orchestrates numerous complex biological processes during development and is critical to the maintenance of tissue integrity and homeostasis in the adult. As it relates to the central nervous system, WNT signaling plays several roles as it relates to neurogenesis, synaptic formation, memory, and learning. Thus, dysfunction of this pathway is associated with multiple diseases and disorders, including several neurodegenerative disorders. Alzheimer's disease (AD) is characterized by several pathologies, synaptic dysfunction, and cognitive decline. In this review, we will discuss the various epidemiological, clinical, and animal studies that demonstrate a precise link between aberrant WNT signaling and AD-associated pathologies. In turn, we will discuss the manner in which WNT signaling influences multiple molecular, biochemical, and cellular pathways upstream of these end-point pathologies. Finally, we will discuss how merging tools and technologies can be used to generate next generation cellular models to dissect the relationship between WNT signaling and AD.

The Flavonol Quercitrin Hinders GSK3 Activity and Potentiates the Wnt/β-Catenin Signaling Pathway

The Wnt/β-catenin signaling pathway dictates cell proliferation and differentiation during embryonic development and tissue homeostasis. Its deregulation is associated with many pathological conditions, including neurodegenerative disease, frequently downregulated. The lack of efficient treatment for these diseases, including Alzheimer’s disease (AD), makes Wnt signaling an attractive target for therapies. Interestingly, novel Wnt signaling activating compounds are less frequently described than inhibitors, turning the quest for novel positive modulators even more appealing. In that sense, natural compounds are an outstanding source of potential drug leads. Here, we combine different experimental models, cell-based approaches, neuronal culture assays, and rodent behavior tests with Xenopus laevis phenotypic analysis to characterize quercitrin, a natural compound, as a novel Wnt signaling potentiator. We find that quercitrin potentiates the signaling in a concentration-dependent manner and increases the occurrence of the Xenopus secondary axis phenotype mediated by Xwnt8 injection. Using a GSK3 biosensor, we describe that quercitrin impairs GSK3 activity and increases phosphorylated GSK3β S9 levels. Treatment with XAV939, an inhibitor downstream of GSK3, impairs the quercitrin-mediated effect. Next, we show that quercitrin potentiates the Wnt3a-synaptogenic effect in hippocampal neurons in culture, which is blocked by XAV939. Quercitrin treatment also rescues the hippocampal synapse loss induced by intracerebroventricular injection of amyloid-β oligomers (AβO) in mice. Finally, quercitrin rescues AβO-mediated memory impairment, which is prevented by XAV939. Thus, our study uncovers a novel function for quercitrin as a Wnt/β-catenin signaling potentiator, describes its mechanism of action, and opens new avenues for AD treatments.

Molecular Insights to the Wnt Signaling During Alzheimer's Disorder: a Potential Target for Therapeutic Interventions

In the adult brain, Wnt signaling is crucial for neurogenesis, and it also regulates neuronal development, neuronal maturation, neuronal differential, and proliferation. Impaired Wnt signaling pathways are associated with enhanced levels of amyloid-β, reduced β-catenin levels, and increased expression of GSK-3β enzyme, suggesting its direct association with the pathogenesis of Alzheimer's disorder (AD). These findings are consolidated by reports where activation of Wnt signaling by genetic factors and pharmacological intervention has improved the cognitive functions in animals and restored neurogenesis in the adult brain. Various natural and synthetic molecules have been identified that modulate Wnt signaling in the adult brain and promote neurogenesis and alleviate behavioral dysfunction. These molecules include lithium, valproic acid, ethosuximide, selenomethionine, curcumin, andrographolide, xanthoceraside, huperzine A, pyridostigmine, ginkgolide-B, ricinine, cannabidiol, and resveratrol. These molecules are associated with the DKK1 and GSK-3β inhibition and β-catenin stabilization along with their effects on neurogenesis, neuronal proliferation, and differentiation in the hippocampus through modulation of Wnt signaling and thereby could prove beneficial in the management of AD pathogenesis. Although modulation of the Wnt signaling seems to suggest to be promising in the management of AD, unfortunately, most of the literature available for the association of Wnt signaling and AD pathogenesis is either from preclinical studies or post-mortem brain. Therefore, it will be interesting to understand the role of Wnt signaling in AD patients, and a rigorous investigation could provide us with a better understanding of AD pathogenesis and the identification of novel targets for therapeutic interventions.

Primary cilia and ciliary signaling pathways in aging and age-related brain disorders

Brain disorders are characterized by the progressive loss of structure and function of the brain as a consequence of progressive degeneration and/or death of nerve cells. Aging is a major risk factor for brain disorders such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and stroke. Various cellular and molecular events have been shown to play a role in the progress of neurodegenerative diseases. Emerging studies suggest that primary cilia could be a key regulator in brain diseases. The primary cilium is a singular cellular organelle expressed on the surface of many cell types, such as astrocytes and neurons in the mature brain. Primary cilia detect extracellular cues, such as Sonic Hedgehog (SHH) protein, and transduce these signals into cells to regulate various signaling pathways. Abnormalities in ciliary length and frequency (ratio of ciliated cells) have been implicated in various human diseases, including brain disorders. This review summarizes current findings and thoughts on the role of primary cilia and ciliary signaling pathways in aging and age-related brain disorders.

Role of Wnt signaling in synaptic plasticity and memory

Ever since their discoveries, the Wnt pathways have been consistently associated with key features of cellular development, including metabolism, structure and cell fate. The three known pathways (the canonical Wnt/β-catenin and the two non-canonical Wnt/Ca⁺⁺ and Wnt/JNK/PCP pathways) participate in complex networks of interaction with a wide range of regulators of cell function, such as GSK-3β, AKT, PKC and mTOR, among others. These proteins are known to be involved in the formation and maintenance of memory. Currently, studies with Wnt and memory have shown that the canonical and non-canonical pathways play key roles in different processes associated with memory. So, in this review we briefly summarize the different roles that Wnt signaling can play in neurons and in memory, as well as in Alzheimer's disease, focusing towards animal studies. We start with the molecular characterization of the family and its receptors, as well as the most commonly used drugs for pharmacological manipulations. Next, we describe its role in synaptic plasticity and memory, and how the regulations of these pathways affect crucial features of neuronal function. Furthermore, we succinctly present the current knowledge on how the Wnt pathways are implicated in Alzheimer's disease, and how studies are seeing them as a potential candidate for effective treatments. Lastly, we point toward challenges of Wnt research, and how knowledge on these pathways can lead towards a better understanding of neurobiological and pathological processes.

Repositioning of antidiabetic drugs for Alzheimer's disease: possibility of Wnt signaling modulation by targeting LRP6 an in silico based study

Alzheimer disease (AD) is the most common, irreversible and progressive form of dementia for which the exact pathology and cause are still not clear. At present, we are only confined to symptomatic treatment, and the lack of disease-modifying therapeutics is worrisome. Alteration of Wnt signaling has been linked to metabolic diseases as well as AD. The crosstalk between Canonical Wnt signaling and insulin signaling pathway has been widely studied and accepted from several clinical and preclinical studies that have proven the beneficial effect of antidiabetic medications in the case of memory and cognition loss. This structure-based in silico study was focused on exploring the link between the currently available FDA approved antidiabetic drugs and the Wnt signaling pathway. The library of antidiabetics was obtained from drug bank and was screened for their binding affinity with protein (PDB ID: 3S2K) LRP6, a coreceptor of the Wnt signaling pathway using GLIDE module of Schrodinger. The top molecules, with higher docking score, binding energy and stable interactions, were subjected to energy-based calculation using MMGBSA, followed by a molecular dynamics-based simulation study. Drugs of class α-glucosidase inhibitors and peroxisome proliferator-activated receptors (PPARs) agonists were found to have a strong affinity towards LRP6 proteins, highlighting the possibility of the modulation of Wnt signaling by antidiabetics as one of the possible mechanisms for use in AD. However, further experimental based in vitro and in vivo studies are warranted for verification and support.Communicated by Ramaswamy H. Sarma.

Interaction of NF-κB and Wnt/β-catenin Signaling Pathways in Alzheimer's Disease and Potential Active Drug Treatments

The most important neuropathological features of Alzheimer's disease (AD) are extracellular amyloid-β protein (Aβ) deposition, tau protein hyperphosphorylation and activation of neurometabolic reaction in the brain accompanied by neuronal and synaptic damage, and impaired learning and memory function. According to the amyloid cascade hypothesis, increased Aβ deposits in the brain to form the core of the senile plaques that initiate cascade reactions, affecting the synapses and stimulating activation of microglia, resulting in neuroinflammation. A growing number of studies has shown that NF-κB and Wnt/β-catenin pathways play important roles in neurodegenerative diseases, especially AD. In this review, we briefly introduce the connection between neuroinflammation-mediated synaptic dysfunction in AD and elaborated on the mechanism of these two signaling pathways in AD-related pathological changes, as well as their interaction. Based on our interest in natural compounds, we also briefly introduce and conduct preliminary screening of potential therapeutics for AD.

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.

Hormetic-Like Effects of L-Homocysteine on Synaptic Structure, Function, and Aβ Aggregation

Alzheimer’s Disease (AD) is the primary cause of dementia among the elderly population. Elevated plasma levels of homocysteine (HCy), an amino acid derived from methionine metabolism, are considered a risk factor and biomarker of AD and other types of dementia. An increase in HCy is mostly a consequence of high methionine and/or low vitamin B intake in the diet. Here, we studied the effects of physiological and pathophysiological HCy concentrations on oxidative stress, synaptic protein levels, and synaptic activity in mice hippocampal slices. We also studied the in vitro effects of HCy on the aggregation kinetics of Aβ₄₀. We found that physiological cerebrospinal concentrations of HCy (0.5 µM) induce an increase in synaptic proteins, whereas higher doses of HCy (30–100 µM) decrease their levels, thereby increasing oxidative stress and causing excitatory transmission hyperactivity, which are all considered to be neurotoxic effects. We also observed that normal cerebrospinal concentrations of HCy slow the aggregation kinetic of Aβ₄₀, whereas high concentrations accelerate its aggregation. Finally, we studied the effects of HCy and HCy + Aβ₄₂ over long-term potentiation. Altogether, by studying an ample range of effects under different HCy concentrations, we report, for the first time, that HCy can exert beneficial or toxic effects over neurons, evidencing a hormetic-like effect. Therefore, we further encourage the use of HCy as a biomarker and modifiable risk factor with therapeutic use against AD and other types of dementia.

Restoring Wnt/β-catenin signaling is a promising therapeutic strategy for Alzheimer's disease

Alzheimer’s disease (AD) is an aging-related neurological disorder characterized by synaptic loss and dementia. Wnt/β-catenin signaling is an essential signal transduction pathway that regulates numerous cellular processes including cell survival. In brain, Wnt/β-catenin signaling is not only crucial for neuronal survival and neurogenesis, but it plays important roles in regulating synaptic plasticity and blood-brain barrier integrity and function. Moreover, activation of Wnt/β-catenin signaling inhibits amyloid-β production and tau protein hyperphosphorylation in the brain. Critically, Wnt/β-catenin signaling is greatly suppressed in AD brain via multiple pathogenic mechanisms. As such, restoring Wnt/β-catenin signaling represents a unique opportunity for the rational design of novel AD therapies.

Dickkopf-1 blocks 17β-estradiol-enhanced object memory consolidation in ovariectomized female mice

The memory-enhancing effects of 17β-estradiol (E₂) depend upon rapid activation of several cell-signaling cascades within the dorsal hippocampus (DH). Among the many cell-signaling pathways that mediate memory processes, Wnt/β-catenin signaling has emerged as a potential key player because of its importance to hippocampal development and synaptic plasticity. However, whether E₂ interacts with Wnt/β-catenin signaling to promote memory consolidation is unknown. Therefore, the present study examined whether Wnt/β-catenin signaling within the DH is necessary for E₂-induced memory consolidation in ovariectomized mice tested in the object recognition and object placement tasks. Ovariectomized C57BL/6 mice received immediate post-training infusions of E₂ or vehicle into the dorsal third ventricle plus the endogenous Wnt/β-catenin antagonist Dickkopf-1 (Dkk-1) or vehicle into the DH to assess whether the memory-enhancing effects of E₂ depend on activation of Wnt/β-catenin signaling. Our results suggest that Dkk-1 blocks E₂-induced memory enhancement as hypothesized, but may do so by only moderately blunting Wnt/β-catenin signaling while concurrently activating Wnt/JNK signaling. The current study provides novel insights into the mechanisms through which E₂ enhances memory consolidation in the DH, as well as critical information about the mechanistic actions of Dkk-1.

Hypothyroidism and Cognitive Disorders during Development and Adulthood: Implications in the Central Nervous System

Thyroid hormones (THs) play a critical function in fundamental signaling of the body regulating process such as metabolism of glucose and lipids, cell maturation and proliferation, and neurogenesis, to name just a few. THs trigger biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). For years, a close relationship between the THs hormones and the central nervous system (CNS) has been described, not only for neuronal cells but also for glial development and differentiation. A deficit in thyroid hormones triiodothyronine (T₃) and thyroxine (T₄) is observed in the hypothyroid condition, generated by a iodine deficiency or an autoimmune response of the body. In the hypothyroid condition, several cellular deregulation and alterations have been described in dendrite spine morphology, cell migration and proliferation, and impaired synaptic transmission in the hippocampus, among others. The aim of this review is to describe the role of the thyroid hormones with focus in brain function and neurodegenerative disorders.

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.

Anti-aggregant tau mutant promotes neurogenesis

BACKGROUND

The microtubule-associated protein Tau plays a role in neurodegeneration as well as neurogenesis. Previous work has shown that the expression of the pro-aggregant mutant Tau repeat domain causes strong aggregation and pronounced neuronal loss in the hippocampus whereas the anti-aggregant form has no deleterious effects. These two proteins differ mainly in their propensity to form ß structure and hence to aggregate.

METHODS

To elucidate the basis of these contrasting effects, we analyzed organotypic hippocampal slice cultures (OHSCs) from transgenic mice expressing the repeat domain (RD) of Tau with the anti-aggregant mutation (Tau^RDΔKPP) and compared them with slices containing pro-aggregant Tau^RDΔK. Transgene expression in the hippocampus was monitored via a sensitive bioluminescence reporter gene assay (luciferase).

RESULTS

The expression of the anti-aggregant Tau^RDΔKPP leads to a larger volume of the hippocampus at a young age due to enhanced neurogenesis, resulting in an increase in neuronal number. There were no signs of activation of microglia and astrocytes, indicating the absence of an inflammatory reaction. Investigation of signaling pathways showed that Wnt-5a was strongly decreased whereas Wnt3 was increased. A pronounced increase in hippocampal stem cell proliferation (seen by BrdU) was observed as early as P8, in the CA regions where neurogenesis is normally not observed. The increase in neurons persisted up to 16 months of age.

CONCLUSION

The data suggest that the expression of anti-aggregant Tau^RDΔKPP enhances hippocampal neurogenesis mediated by the canonical Wnt signaling pathway, without an inflammatory reaction. This study points to a role of tau in brain development and neurogenesis, in contrast to its detrimental role in neurodegeneration at later age.

Lentiviral Modulation of Wnt/β-Catenin Signaling Affects In Vivo LTP

Wnt signaling is involved in hippocampal development and synaptogenesis. Numerous recent studies have been focused on the role of Wnt ligands in the regulation of synaptic plasticity. Inhibitors and activators of canonical Wnt signaling were demonstrated to decrease or increase, respectively, in vitro long-term potentiation (LTP) maintenance in hippocampal slices (Chen et al. in J Biol Chem 281:11910-11916, 2006; Vargas et al. in J Neurosci 34:2191-2202, 2014, Vargas et al. in Exp Neurol 264:14-25, 2015). Using lentiviral approach to down- and up-regulate the canonical Wnt signaling, we explored whether Wnt/β-catenin signaling is critical for the in vivo LTP. Chronic suppression of Wnt signaling induced an impairment of in vivo LTP expression 14 days after lentiviral suspension injection, while overexpression of Wnt3 was associated with a transient enhancement of in vivo LTP magnitude. Both effects were related to the early phase LTP and did not affect LTP maintenance. A loss-of-function study demonstrated decreased initial paired pulse facilitation ratio, β-catenin, and phGSK-3β levels. A gain-of-function study revealed not only an increase in PSD-95, β-catenin, and Cyclin D1 protein levels, but also a reduced phGSK-3β level and enhanced GSK-3β kinase activity. These results suggest a presynaptic dysfunction predominantly underlying LTP impairment while postsynaptic modifications are primarily involved in transient LTP amplification. This study is the first demonstration of the involvement of Wnt/β-catenin signaling in synaptic plasticity regulation in an in vivo LTP model.

The neurotoxicity of amyloid β-protein oligomers is reversible in a primary neuron model

Alzheimer’s disease (AD) is characterized by the accumulation of extracellular amyloid β-protein (Aβ) and intracellular hyperphosphorylated tau proteins. Recent evidence suggests that soluble Aβ oligomers elicit neurotoxicity and synaptotoxicity, including tau abnormalities, and play an initiating role in the development of AD pathology. In this study, we focused on the unclarified issue of whether the neurotoxicity of Aβ oligomers is a reversible process. Using a primary neuron culture model, we examined whether the neurotoxic effects induced by 2-day treatment with Aβ42 oligomers (Aβ-O) are reversible during a subsequent 2-day withdrawal period. Aβ-O treatment resulted in activation of caspase-3 and eIF2α, effects that were considerably attenuated following Aβ-O removal. Immunocytochemical analyses revealed that Aβ-O induced aberrant phosphorylation and caspase-mediated cleavage of tau, both of which were mostly reversed by Aβ-O removal. Furthermore, Aβ-O caused intraneuronal dislocation of β-catenin protein and a reduction in its levels, and these alterations were partially reversed upon Aβ-O withdrawal. The dislocation of β-catenin appeared to reflect synaptic disorganization. These findings indicate that removal of extracellular Aβ-O can fully or partially reverse Aβ-O-induced neurotoxic alterations in our neuron model. Accordingly, we propose that the induction of neurotoxicity by Aβ oligomers is a reversible process, which has important implications for the development of AD therapies.

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.

Wnt5a Increases the Glycolytic Rate and the Activity of the Pentose Phosphate Pathway in Cortical Neurons

In the last few years, several reports have proposed that Wnt signaling is a general metabolic regulator, suggesting a role for this pathway in the control of metabolic flux. Wnt signaling is critical for several neuronal functions, but little is known about the correlation between this pathway and energy metabolism. The brain has a high demand for glucose, which is mainly used for energy production. Neurons use energy for highly specific processes that require a high energy level, such as maintaining the electrical potential and synthesizing neurotransmitters. Moreover, an important metabolic impairment has been described in all neurodegenerative disorders. Despite the key role of glucose metabolism in the brain, little is known about the cellular pathways involved in regulating this process. We report here that Wnt5a induces an increase in glucose uptake and glycolytic rate and an increase in the activity of the pentose phosphate pathway; the effects of Wnt5a require the intracellular generation of nitric oxide. Our data suggest that Wnt signaling stimulates neuronal glucose metabolism, an effect that could be important for the reported neuroprotective role of Wnt signaling in neurodegenerative disorders.

Curcumin Rescues Diabetic Renal Fibrosis by Targeting Superoxide-Mediated Wnt Signaling Pathways

The purposes of this study were to investigate whether curcumin can weaken diabetic nephropathy by modulating both oxidative stress and renal injury from Wnt signaling mediation. Wnt5a/β-catenin depression and induction of superoxide synthesis are associated with high glucose (HG) induced transforming growth factor (TGF)-β1 and fibronectin expression in mesangial cells. Curcumin resumes HG depression of Wnt/β-catenin signaling and alleviates HG induction of superoxide, TGF-β1 and fibronectin expression in renal mesangial cell. Exogenous curcumin alleviated urinary total proteinuria and serum superoxide level in diabetic rats. Based on laser-captured microdissection for quantitative real-time polymerase chain reaction, it was found that diabetes significantly increased TGF-β1 and fibronectin expression in line with depressed Wnt5a expression. Curcumin treatment reduced the TGF-β1 and fibronectin activation and the inhibiting effect of diabetes on Wnt5a/β-catenin expression in renal glomeruli. Immunohistochemistry showed that curcumin treatment significantly reduced 8-hydroxy-2'-deoxyguanosine, TGF-β1 and fibronectin, and was in line with the restoration of the suppressed Wnt5a expression immunoreactivities in glomeruli of diabetic rats. Curcumin alleviated extracellular matrix accumulation in diabetic nephropathy by not only preventing the diabetes-mediated superoxide synthesis but also resuming downregulation of Wnt/β-catenin signaling. These findings suggest that regulation of Wnt activity by curcumin is a feasible alternative strategy to rescue diabetic renal injury.

The increased potassium intake improves cognitive performance and attenuates histopathological markers in a model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by hallmarks that include an accumulation of amyloid-β peptide (Aβ), inflammation, oxidative stress and synaptic dysfunction, which lead to a decrease in cognitive function. To date, the onset and progression of AD have been associated with pathologies such as hypertension and diabetes. Hypertension, a disease with a high incidence worldwide, is characterized by a chronic increase in blood pressure. Interestingly, this disease has a close relationship to the eating behavior of patients because high Na(+) intake is a significant risk factor for hypertension. In fact, a decrease in Na(+) consumption, along with an increase in K(+) intake, is a primary non-pharmacological approach to preventing hypertension. In the present work, we examined whether an increase in K(+) intake affects the expression of certain neuropathological markers or the cognitive performance of a murine model of AD. We observed that an increase in K(+) intake leads to a change in the aggregation pattern of the Aβ peptide, a partial decrease in some epitopes of tau phosphorylation and improvement in the cognitive performance. The recovery in cognitive performance was correlated with a significant improvement in the generation of long-term potentiation. We also observed a decrease in markers related to inflammation and oxidative stress such as glial fibrillary acidic protein (GFAP), interleukin 6 (IL-6) and 4-hydroxynonenal (4-HNE). Together, our data support the idea that changes in diet, such as an increase in K(+) intake, may be important in the prevention of AD onset as a non-pharmacological therapy.