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

The Roles of the Stem Cell-Controlling Sox2 Transcription Factor: from Neuroectoderm Development to Alzheimer's Disease?

Sox2 is a component of the core transcriptional regulatory network which maintains the totipotency of the cells during embryonic preimplantation period, the pluripotency of embryonic stem cells, and the multipotency of neural stem cells. This maintenance is controlled by internal loops between Sox2 and other transcription factors of the core such as Oct4, Nanog, Dax1, and Klf4, downstream proteins of extracellular ligands, epigenetic modifiers, and miRNAs. As Sox2 plays an important role in the balance between stem cells maintenance and commitment to differentiated lineages throughout the lifetime, it is supposed that Sox2 could regulate stem cells aging processes. In this review, we provide an update concerning the involvement of Sox2 in neurogenesis during normal aging and discuss its possible role in Alzheimer's disease.

Identifying genetic interactions associated with late-onset Alzheimer's disease

Background

Identifying genetic interactions in data obtained from genome-wide association studies (GWASs) can help in understanding the genetic basis of complex diseases. The large number of single nucleotide polymorphisms (SNPs) in GWASs however makes the identification of genetic interactions computationally challenging. We developed the Bayesian Combinatorial Method (BCM) that can identify pairs of SNPs that in combination have high statistical association with disease.

Results

We applied BCM to two late-onset Alzheimer’s disease (LOAD) GWAS datasets to identify SNPs that interact with known Alzheimer associated SNPs. We also compared BCM with logistic regression that is implemented in PLINK. Gene Ontology analysis of genes from the top 200 dataset SNPs for both GWAS datasets showed overrepresentation of LOAD-related terms. Four genes were common to both datasets: APOE and APOC1, which have well established associations with LOAD, and CAMK1D and FBXL13, not previously linked to LOAD but having evidence of involvement in LOAD. Supporting evidence was also found for additional genes from the top 30 dataset SNPs.

Conclusion

BCM performed well in identifying several SNPs having evidence of involvement in the pathogenesis of LOAD that would not have been identified by univariate analysis due to small main effect. These results provide support for applying BCM to identify potential genetic variants such as SNPs from high dimensional GWAS datasets.

Electronic supplementary material

The online version of this article (doi:10.1186/s13040-014-0035-z) contains supplementary material, which is available to authorized users.

The effect of deficient muscarinic signaling on commonly reported biochemical effects in schizophrenia and convergence with genetic susceptibility loci in explaining symptom dimensions of psychosis

With the advent of DSM 5 criticism has generally centered on a lack of biological validity of the diagnostic criteria. Part of the problem in describing a nosology of psychosis is the tacit assumption of multiple genetic causes each with an incremental loading on the clinical picture that fails to differentiate a clear underlying pathophysiology of high impact. The aim of this paper is to consolidate a primary theory of deficient muscarinic signaling underlying key clinical features of schizophrenia and its regulation by several important genetic associations including neuregulin, DISC and dysbindin. Secondary reductions in markers for GABAergic function and changes in the levels of interneuron calcium binding proteins parvalbumin and calbindin can be attributed to dysfunctional muscarinic transduction. A parallel association exists for cytokine production. The convergent pathway hypothesis is likewise used to model dopaminergic and glutamatergic theories of schizophrenia. The negative symptom dimension is correlated with dysfunction of Akt and ERK transduction, a major point of convergence. The present paradigm predicts the importance of a recent finding of a deletion in a copy number variant of PLCB1 and its potential use if replicated, as one of the first testable biological markers differentiating schizophrenia from bipolar disorder and further subtyping of schizophrenia into deficit and non-deficit. Potential limitations of PLCB1 as a prospective marker are also discussed.

Activation of PPAR gamma receptors reduces levodopa-induced dyskinesias in 6-OHDA-lesioned rats

Long-term administration of l-3,4-dihydroxyphenylalanine (levodopa), the mainstay treatment for Parkinson's disease (PD), is accompanied by fluctuations in its duration of action and motor complications (dyskinesia) that dramatically affect the quality of life of patients. Levodopa-induced dyskinesias (LID) can be modeled in rats with unilateral 6-OHDA lesions via chronic administration of levodopa, which causes increasingly severe axial, limb, and orofacial abnormal involuntary movements (AIMs) over time. In previous studies, we showed that the direct activation of CB1 cannabinoid receptors alleviated rat AIMs. Interestingly, elevation of the endocannabinoid anandamide by URB597 (URB), an inhibitor of endocannabinoid catabolism, produced an anti-dyskinetic response that was only partially mediated via CB1 receptors and required the concomitant blockade of transient receptor potential vanilloid type-1 (TRPV1) channels by capsazepine (CPZ) (Morgese et al., 2007). In this study, we showed that the stimulation of peroxisome proliferator-activated receptors (PPAR), a family of transcription factors activated by anandamide, contributes to the anti-dyskinetic effects of URB+CPZ, and that the direct activation of the PPARγ subtype by rosiglitazone (RGZ) alleviates levodopa-induced AIMs in 6-OHDA rats. AIM reduction was associated with an attenuation of levodopa-induced increase of dynorphin, zif-268, and of ERK phosphorylation in the denervated striatum. RGZ treatment did not decrease striatal levodopa and dopamine bioavailability, nor did it affect levodopa anti-parkinsonian activity. Collectively, these data indicate that PPARγ may represent a new pharmacological target for the treatment of LID.

Wnts are expressed in the spinal cord of adult mice and are differentially induced after injury

The Wnt family of proteins plays key roles during central nervous system development and has been involved in several neuropathologies during adulthood, including spinal cord injury (SCI). However, Wnts expression knowledge is relatively limited during adult stages. Here, we sought to define the Wnt family expression pattern after SCI in adult mice by using quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC). Under physiological conditions, the messenger RNAs (mRNAs) of most Wnt ligands, inhibitors, receptors, and coreceptors are constitutively expressed in healthy adult mice. After dorsal hemisection, we found significant time-dependent variations, with a prominent up-regulation of Wnt inhibitory factor 1 (Wif1). IHC against Frizzled (Fz) 1 and Fz4, as representatives of late and acute up-regulated receptors, showed a differential expression in the uninjured spinal cord of Fz1 by neurons and oligodendrocytes and Fz4 by astrocytes. After injury, both receptors were maintained in the same type of cells. Finally, by using BATgal reporter mice, our results revealed active β-catenin signaling in neurons of the dorsal horn and cells of the central canal of uninjured spinal cords, besides a lack of additional SCI-induced activation. In conclusion, we demonstrate Wnt expression in the adult spinal cord of mice that is modulated by SCI, which differs from that previously described in rats. Further, Fz receptors are differentially expressed by neurons and glial cells, suggestive for cell-specific patterns and thus diverse physiological roles. Further studies will help toward in-depth characterization of the role of all Wnt factors and receptors described and eventually allow for the design of novel therapies.

Circadian rhythms, Wnt/beta-catenin pathway and PPAR alpha/gamma profiles in diseases with primary or secondary cardiac dysfunction

Circadian clock mechanisms are far-from-equilibrium dissipative structures. Peroxisome proliferator-activated receptors (PPAR alpha, beta/delta, and gamma) play a key role in metabolic regulatory processes, particularly in heart muscle. Links between circadian rhythms (CRs) and PPARs have been established. Mammalian CRs involve at least two critical transcription factors, CLOCK and BMAL1 (Gekakis et al., 1998; Hogenesch et al., 1998). PPAR gamma plays a major role in both glucose and lipid metabolisms and presents circadian properties which coordinate the interplay between metabolism and CRs. PPAR gamma is a major component of the vascular clock. Vascular PPAR gamma is a peripheral regulator of cardiovascular rhythms controlling circadian variations in blood pressure and heart rate through BMAL1. We focused our review on diseases with abnormalities of CRs and with primary or secondary cardiac dysfunction. Moreover, these diseases presented changes in the Wnt/beta-catenin pathway and PPARs, according to two opposed profiles. Profile 1 was defined as follows: inactivation of the Wnt/beta-catenin pathway with increased expression of PPAR gamma. Profile 2 was defined as follows: activation of the Wnt/beta-catenin pathway with decreased expression of PPAR gamma. A typical profile 1 disease is arrhythmogenic right ventricular cardiomyopathy, a genetic cardiac disease which presents mutations of the desmosomal proteins and is mainly characterized by fatty acid accumulation in adult cardiomyocytes mainly in the right ventricle. The link between PPAR gamma dysfunction and desmosomal genetic mutations occurs via inactivation of the Wnt/beta-catenin pathway presenting oscillatory properties. A typical profile 2 disease is type 2 diabetes, with activation of the Wnt/beta-catenin pathway and decreased expression of PPAR gamma. CRs abnormalities are present in numerous pathologies such as cardiovascular diseases, sympathetic/parasympathetic dysfunction, hypertension, diabetes, neurodegenerative diseases, cancer which are often closely inter-related.

Deficiency in LRP6-mediated Wnt signaling contributes to synaptic abnormalities and amyloid pathology in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurological disorder characterized by synaptic loss and dementia. The low-density lipoprotein receptor-related protein 6 (LRP6) is an essential coreceptor for Wnt signaling, and its genetic variants have been linked to AD risk. Here we report that neuronal LRP6-mediated Wnt signaling is critical for synaptic function and cognition. Conditional deletion of Lrp6 gene in mouse forebrain neurons leads to age-dependent deficits in synaptic integrity and memory. Neuronal LRP6 deficiency in an amyloid mouse model also leads to exacerbated amyloid pathology due to increased APP processing to amyloid-β. In humans, LRP6 and Wnt signaling are significantly downregulated in AD brains, likely by a mechanism that depends on amyloid-β. Our results define a critical pathway in which decreased LRP6-mediated Wnt signaling, synaptic dysfunction, and elevated Aβ synergistically accelerate AD progression and suggest that restoring LRP6-mediated Wnt signaling can be explored as a viable strategy for AD therapy.

Brain metabolite clearance: impact on Alzheimer's disease

Alzheimer's Disease (AD) is a complex neurodegenerative disorder often associated with aging and characterized by several critical molecular changes that take place in the brain. Among the molecular hallmarks of AD, increased levels of amyloid β-peptide (Aβ) and the subsequent Aβ-derived damage are the most well-studied factors; however, despite the large amounts of effort and resources devoted to the study of AD and AD pathophysiology, the scientific community still awaits therapeutic alternatives capable of ensuring a better outcome for AD patients. In 2012, Cramer et al. (Science 335:1503-1506 2012) astonished the scientific community by rescuing behavioral and cognitive impairments in AD mouse models via oral administration of bexarotene, a drug used to treat some types of skin cancer. Moreover, these authors demonstrated that bexarotene, a retinoid X receptor (RXR) agonist, exerts major effects on Aβ levels, mainly through increased apolipoprotein E (ApoE) expression. Apart from the valid questions addressed in Cramer's work, only a few attempts have been made to explain the effects of bexarotene. Most of these explanations have been solely based on the ability of bexarotene to reduce Aβ levels and not on the mechanisms that lead to such a reduction. Although it is well known that an imbalance in the Aβ production/excretion rate is the basis of increased Aβ levels in AD, no further explanations have been proposed to address the potential involvement of the blood-brain barrier (BBB), a critical Aβ-clearance structure, in the bexarotene-mediated effects. Moreover, no attempt has been made to explain how the different effects observed after bexarotene administration are connected to each other. Based on current information and on our own experience with nuclear receptors (NR), we offer new perspectives on the mechanisms of bexarotene action, which should help to improve our knowledge of NRs.

Derailed intraneuronal signalling drives pathogenesis in sporadic and familial Alzheimer's disease

Although a wide variety of genetic and nongenetic Alzheimer's disease (AD) risk factors have been identified, their role in onset and/or progression of neuronal degeneration remains elusive. Systematic analysis of AD risk factors revealed that perturbations of intraneuronal signalling pathways comprise a common mechanistic denominator in both familial and sporadic AD and that such alterations lead to increases in Aβ oligomers (Aβo) formation and phosphorylation of TAU. Conversely, Aβo and TAU impact intracellular signalling directly. This feature entails binding of Aβo to membrane receptors, whereas TAU functionally interacts with downstream transducers. Accordingly, we postulate a positive feedback mechanism in which AD risk factors or genes trigger perturbations of intraneuronal signalling leading to enhanced Aβo formation and TAU phosphorylation which in turn further derange signalling. Ultimately intraneuronal signalling becomes deregulated to the extent that neuronal function and survival cannot be sustained, whereas the resulting elevated levels of amyloidogenic Aβo and phosphorylated TAU species self-polymerizes into the AD plaques and tangles, respectively.

Inverse association between cancer and neurodegenerative disease: review of the epidemiologic and biological evidence

Growing evidence suggests an unusual epidemiologic association between cancer and certain neurological conditions, particularly age-related neurodegenerative diseases. Cancer survivors have a 20-50% lower risk of developing Parkinson's and Alzheimer's disease, and patients with these neurodegenerative conditions have a substantially lower incidence of cancer. We review the epidemiologic evidence for this inverse co-morbidity and show that it is not simply an artifact of survival bias or under-diagnosis. We then review the potential biological explanations for this association, which is intimately linked to the very different nature of dividing cells and neurons. The known genetic and metabolic connections between cancer and neurodegeneration generally fall within two categories. The first includes shared genes and pathways such as Pin1 and the ubiquitin proteasome system that are dysregulated in different directions to cause one disease or the other. The second includes common pathophysiological mechanisms such as mitochondrial dysfunction, oxidative stress and DNA damage that drive both conditions, but with different cellular fates. We discuss examples of these biological links and their implications for developing new approaches to prevention and treatment of both diseases.

Is Alzheimer's disease related to metabolic syndrome? A Wnt signaling conundrum

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 36 million people worldwide. AD is characterized by a progressive loss of cognitive functions. For years, it has been thought that age is the main risk factor for AD. Recent studies suggest that life style factors, including nutritional behaviors, play a critical role in the onset of dementia. Evidence about the relationship between nutritional behavior and AD includes the role of conditions such as obesity, hypertension, dyslipidemia and elevated glucose levels. The coexistence of some of these cardio-metabolic risk factors is generally known as metabolic syndrome (MS). Some clinical studies support the role of MS in the onset of AD. However, the cross-talk between the molecular signaling implicated in these disorders is unknown. In the present review, we focus on the molecular correlates that support the relationship between MS and the onset of AD. We also discuss relevant issues such as the role of leptin, insulin and renin-angiotensin signaling in the brain and the possible role of Wnt signaling in both MS and AD. We discuss the evidence supporting the use of ob/ob mice, high-fructose diets, aortic coarctation-induced hypertension and Octodon degus, which spontaneously develops β-amyloid deposits and metabolic derangements, as suitable animal models to address the relationships between MS and AD. Finally, we examine emergent data supporting the role of Wnt signaling in the modulation of AD and MS, implicating this pathway as a therapeutic target in both conditions.

Alzheimer's disease: relevant molecular and physiopathological events affecting amyloid-β brain balance and the putative role of PPARs

Alzheimer’s disease (AD) is the most common form of age-related dementia. With the expected aging of the human population, the estimated morbidity of AD suggests a critical upcoming health problem. Several lines of research are focused on understanding AD pathophysiology, and although the etiology of the disease remains a matter of intense debate, increased brain levels of amyloid-β (Aβ) appear to be a critical event in triggering a wide range of molecular alterations leading to AD. It has become evident in recent years that an altered balance between production and clearance is responsible for the accumulation of brain Aβ. Moreover, Aβ clearance is a complex event that involves more than neurons and microglia. The status of the blood-brain barrier (BBB) and choroid plexus, along with hepatic functionality, should be considered when Aβ balance is addressed. Furthermore, it has been proposed that exposure to sub-toxic concentrations of metals, such as copper, could both directly affect these secondary structures and act as a seeding or nucleation core that facilitates Aβ aggregation. Recently, we have addressed peroxisomal proliferator-activated receptors (PPARs)-related mechanisms, including the direct modulation of mitochondrial dynamics through the PPARγ-coactivator-1α (PGC-1α) axis and the crosstalk with critical aging- and neurodegenerative-related cellular pathways. In the present review, we revise the current knowledge regarding the molecular aspects of Aβ production and clearance and provide a physiological context that gives a more complete view of this issue. Additionally, we consider the different structures involved in AD-altered Aβ brain balance, which could be directly or indirectly affected by a nuclear receptor (NR)/PPAR-related mechanism.

Signaling pathway cross talk in Alzheimer's disease

Numerous studies suggest energy failure and accumulative intracellular waste play a causal role in the pathogenesis of several neurodegenerative disorders and Alzheimer's disease (AD) in particular. AD is characterized by extracellular amyloid deposits, intracellular neurofibrillary tangles, cholinergic deficits, synaptic loss, inflammation and extensive oxidative stress. These pathobiological changes are accompanied by significant behavioral, motor, and cognitive impairment leading to accelerated mortality. Currently, the potential role of several metabolic pathways associated with AD, including Wnt signaling, 5' adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), Sirtuin 1 (Sirt1, silent mating-type information regulator 2 homolog 1), and peroxisome proliferator-activated receptor gamma co-activator 1-α (PGC-1α) have widened, with recent discoveries that they are able to modulate several pathological events in AD. These include reduction of amyloid-β aggregation and inflammation, regulation of mitochondrial dynamics, and increased availability of neuronal energy. This review aims to highlight the involvement of these new set of signaling pathways, which we have collectively termed "anti-ageing pathways", for their potentiality in multi-target therapies against AD where cellular metabolic processes are severely impaired.

Mesenchymal Stem Cells Increase Hippocampal Neurogenesis and Neuronal Differentiation by Enhancing the Wnt Signaling Pathway in an Alzheimer's Disease Model

Neurogenesis in the subgranular zone of the hippocampal dentate gyrus may act as an endogenous repair mechanism in Alzheimer's disease (AD), and the Wnt signaling pathway has been suggested to closely modulate neurogenesis in amyloid-β (Aβ)-related AD models. The present study investigated whether mesenchymal stem cells (MSCs) would modulate hippocampal neurogenesis via modulation of the Wnt signaling pathway in a model of AD. In Aβ-treated neuronal progenitor cells (NPCs), the coculture with MSCs increased significantly the expression of Ki-67, GFAP, SOX2, nestin, and HuD compared to Aβ treatment alone. In addition, MSC treatment in Aβ-treated NPCs enhanced the expression of β-catenin and Ngn1 compared to Aβ treatment alone. MSC treatment in Aβ-treated animals significantly increased the number of BrdU-ir cells in the hippocampus at 2 and 4 weeks compared to Aβ treatment alone. In addition, quantitative analysis showed that the number of BrdU and HuD double-positive cells in the dentate gyrus was significantly higher in the MSC-treated group than in controls or after Aβ treatment alone. These results demonstrate that MSC administration significantly augments hippocampal neurogenesis and enhances the differentiation of NPCs into mature neurons in AD models by augmenting the Wnt signaling pathway. The use of MSCs to modulate endogenous adult neurogenesis may have a significant impact on future strategies for AD treatment.

The regulation and deregulation of Wnt signaling by PARK genes in health and disease

Wingless/Int (Wnt) signaling pathways are signal transduction mechanisms that have been widely studied in the field of embryogenesis. Recent work has established a critical role for these pathways in brain development, especially of midbrain dopaminergic neurones. However, the fundamental importance of Wnt signaling for the normal function of mature neurones in the adult central nervous system has also lately been demonstrated by an increasing number of studies. Parkinson's disease (PD) is the second most prevalent neurodegenerative disease worldwide and is currently incurable. This debilitating disease is characterized by the progressive loss of a subset of midbrain dopaminergic neurones in the substantia nigra leading to typical extrapyramidal motor symptoms. The aetiology of PD is poorly understood but work performed over the last two decades has identified a growing number of genetic defects that underlie this condition. Here we review a growing body of data connecting genes implicated in PD--most notably the PARK genes--with Wnt signaling. These observations provide clues to the normal function of these proteins in healthy neurones and suggest that deregulated Wnt signaling might be a frequent pathomechanism leading to PD. These observations have implications for the pathogenesis and treatment of neurodegenerative diseases in general.

Downregulation of the Wnt/β-catenin signaling pathway is involved in manganese-induced neurotoxicity in rat striatum and PC12 cells

Manganese (Mn) is an essential trace element. However, exposure to excessive Mn may cause neurodegenerative disorders called manganism. Accumulating evidence indicated that dysregulation of Wnt/β-catenin signaling was tightly associated with the onset of neurodegenerative disorders. However, whether aberrant Wnt/β-catenin signaling contributes to Mn-induced neurotoxicity remains unknown. The present study investigates the involvement of Wnt/β-catenin signaling in Mn-induced neurotoxicity. Western blot and immunohistochemistry analyses showed a remarkable downregulation of p-Ser9-glycogen synthase kinase-3β (GSK-3β) and β-catenin in rat striatum after Mn exposure. TUNEL assay revealed significant neuronal apoptosis following treatment with 25 mg/kg Mn. Immunofluorescent staining showed that β-catenin was expressed predominantly in neurons, and colocalization of β-catenin and active caspase-3 was observed after Mn exposure. Furthermore, Mn exposure resulted in PC12 cells apoptosis, which was accompanied by reduced levels of cellular β-catenin and p-GSK-3β. Accordingly, the mRNA level of the prosurvival factor survivin, a downstream target gene of β-catenin, was synchronously decreased. More importantly, blockage of GSK-3β activity with the GSK-3β inhibitor lithium chloride could attenuate Mn-induced downregulation of β-catenin and survivin as well as neuronal apoptosis. Overall, the present study demonstrates that downregulation of Wnt/β-catenin signaling pathway may be of vital importance in the neuropathological process of Mn-induced neurotoxicity.

Altered expression of atypical PKC and Ryk in the spinal cord of a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive paralysis due to the selective death of motor neurons of unknown causes. Increasing evidence indicates that Wnt signaling is altered in ALS. In this study, we focused on two non-canonical Wnt signaling components, atypical PKC (aPKC) and a Wnt receptor, Ryk, in a mouse model of ALS, SOD1 (G93A). aPKC mediates Wnt signaling to regulate growth cone guidance, axon differentiation and cell survival. Ryk is a Wnt repulsive receptor that regulates axon guidance and inhibits regeneration after spinal cord injury. aPKC expression was increased in motor neurons of the lumbar spinal cord in SOD1 (G93A) mice at both early and late stages. Interestingly, aPKC was co-localized with SOD1 in motor neuron cell bodies and extracellular aggregates, and aPKC-containing extracellular aggregates increased with disease progression. Biochemical fractionation showed that aPKC protein level was increased in the detergent-insoluble protein fraction in SOD1 (G93A) mice at late stage but decreased in the detergent-soluble fraction at symptomatic stage. These results suggest that aPKC may be sequestered in SOD1 aggregates, impairing its ability to protect motor neurons from death. Ryk expression was also increased in the motor neurons and the white matter in the ventral lumbar spinal cord of mutant SOD1 mice with a peak at early stage. These observations indicate that Wnt/aPKC and Wnt/Ryk signaling are altered in SOD1 (G93A) mice, suggesting that changed Wnt signaling may contribute to neurodegeneration in ALS.

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

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

Wnt pathway regulation by long-term moderate exercise in rat hippocampus

An active lifestyle involving regular exercise reduces the deleterious effects of the aging process. At the cerebral level, both synaptic plasticity and neurogenesis are modulated by exercise, although the molecular mechanisms underlying these effects are not clearly understood. In the mature nervous system, the canonical Wnt (Wnt/β-catenin) signaling pathway is implicated in neuroprotection and synaptic plasticity. Here, we examined whether the Wnt pathway could be modulated in adult male rat hippocampus by long-term moderate exercise (treadmill running) or enrichment (handling/environmental stimulation). Sedentary animals showed higher protein levels of the Wnt antagonist, Dkk-1, the lowest levels being found in the exercised group. Although there was no evidence of any changes in activation of the LRP6 receptor, the total levels of LRP6 were higher in exercised and enriched animals. Analysis of some of the components implicated in the phosphorylation of β-catenin, which leads ultimately to its proteasomal degradation, revealed higher levels and activation of Axin1 and GSK-3α/β respectively in sedentary animals. However neither different phosphorylated forms nor total β-catenin protein levels differed between the experimental groups. Higher protein levels of Axin2 and the antiapoptotic protein, Bcl-2, were found with exercise and handling, whereas the proapototic, Bax, was unaffected. Thus, our results suggest activation of the Wnt pathway not only with moderate exercise, but also with the handling of the animals.

RNA deep sequencing analysis reveals that nicotine restores impaired gene expression by viral proteins in the brains of HIV-1 transgenic rats

Persons infected with HIV-1 often develop neurologic disorders despite receiving highly active anti-retroviral therapy. Although the underlying mechanism is largely undetermined, our previous RNA-seq-based study showed that the expression of many genes was altered in the central nervous system (CNS) of HIV-1 transgenic (HIV-1Tg) rats. Because nicotine, a natural agonist of nicotinic acetylcholine receptors, exhibits a neuroprotective effect, we presently tested the hypothesis that nicotine restores the expression of altered genes in the CNS of HIV-1Tg rats. Adult male HIV-1Tg and F344 control strain rats were injected with either nicotine (0.25 mg/kg) or saline subcutaneously twice a day for 17 days. Gene expression in the prefrontal cortex (PFC), dorsal hippocampus (HIP), and dorsal striatum (STR) was evaluated using the RNA deep sequencing technique. We found that about 20% of the altered genes in the HIV-1Tg rat were affected by nicotine in each brain region, with the expression of most restored. Analysis of the restored genes showed distinct pathways corrected by nicotine in different brain regions of HIV-1Tg rats. Specifically, the two most significantly restored pathways were Wnt/β-catenin signaling and ephrin B signaling in the PFC, cAMP-responsive element-binding protein (CREB) signaling and glutathione metabolism pathway in the HIP, and tricarboxylic acid (TCA) cycle and calcium signaling in the STR. Together, our findings indicate that cholinergic modulators such as nicotine have beneficial effects on HIV-1-induced neurologic deficits.

WNT signaling in neuronal maturation and synaptogenesis

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

LRRK2: an éminence grise of Wnt-mediated neurogenesis?

The importance of leucine-rich repeat kinase 2 (LRRK2) to mature neurons is well-established, since mutations in PARK8, the gene encoding LRRK2, are the most common known cause of Parkinson’s disease. Nonetheless, despite the LRRK2 knockout mouse having no overt neurodevelopmental defect, numerous lines of in vitro data point toward a central role for this protein in neurogenesis. Roles for LRRK2 have been described in many key processes, including neurite outgrowth and the regulation of microtubule dynamics. Moreover, LRRK2 has been implicated in cell cycle control, suggesting additional roles in neurogenesis that precede terminal differentiation. However, we contend that the suggested function of LRRK2 as a scaffolding protein at the heart of numerous Wnt signaling cascades provides the most tantalizing link to neurogenesis in the developing brain. Numerous lines of evidence show a critical requirement for multiple Wnt pathways in the development of certain brain regions, not least the dopaminergic neurons of the ventral mid-brain. In conclusion, these observations indicate a function of LRRK2 as a subtle yet critical mediator of the action of Wnt ligands on developing neurons. We suggest that LRRK2 loss- or gain-of-function are likely modifiers of developmental phenotypes seen in animal models of Wnt signaling deregulation, a hypothesis that can be tested by cross-breeding relevant genetically modified experimental strains.

Axonal translation of β-catenin regulates synaptic vesicle dynamics

Many presynaptic transcripts have been observed in axons, yet their role in synapse development remains unknown. Using visually and pharmacologically isolated presynaptic terminals from dissociated rat hippocampal neurons, we found that ribosomes and β-catenin mRNA preferentially localize to recently formed boutons. Locally translated β-catenin accumulates at presynaptic terminals, where it regulates synaptic vesicle release dynamics. Thus, local translation of β-catenin is a newly described mechanism for axons to independently functionalize nerve terminals at great distances from cellular somata.

The Ryk receptor is expressed in glial and fibronectin-expressing cells after spinal cord injury

Wnt proteins play a critical role in central nervous system development and have been implicated in several neuropathologies, including spinal cord injury (SCI). Ryk, an unconventional Wnt receptor, regulates axonal regeneration after SCI, although its expression pattern in this neuropathology remains unclear. Therefore, we sought to define the spatiotemporal and cellular pattern of Ryk expression after a contusive SCI in adult rats using quantitative reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunohistochemical analysis. Under physiological conditions, Ryk is expressed in neurons, astrocytes, and blood vessels, but not in oligodendrocytes, microglia, NG2+ glial precursor cells, or axonal projections. Following SCI, we observed an increase in Ryk mRNA expression from 24 h post-injury until 7 days post-injury, whereas its protein levels were significantly augmented at 7 and 14 days post-injury. Moreover, the spatial and cellular Ryk expression pattern was altered in the damaged tissue, where this receptor was observed in reactive astrocytes and microglia/macrophages, NG2+ glial precursors, fibronectin+ cells, oligodendrocytes, and axons. In conclusion, we demonstrate that Ryk is expressed in the unlesioned spinal cord and that, after SCI, its spatiotemporal and cellular expression pattern changed dramatically, being expressed in cells involved in the spinal cord response to damage.

Uncovering novel actors in astrocyte-neuron crosstalk in Parkinson's disease: the Wnt/β-catenin signaling cascade as the common final pathway for neuroprotection and self-repair

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by progressive loss of dopaminergic (DAergic) neuronal cell bodies in the substantia nigra pars compacta and gliosis. The cause and mechanisms underlying the demise of nigrostriatal DAergic neurons are ill-defined, but interactions between genes and environmental factors are recognized to play a critical role in modulating the vulnerability to PD. Current evidence points to reactive glia as a pivotal factor in PD pathophysiology, playing both protective and destructive roles. Here, the contribution of reactive astrocytes and their ability to modulate DAergic neurodegeneration, neuroprotection and neurorepair in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rodent model of PD will be discussed in the light of novel emerging evidence implicating wingless-type mouse mammary tumor virus integration site (Wnt)/β-catenin signaling as a strong candidate in MPTP-induced nigrostriatal DAergic plasticity. In this work, we highlight an intrinsic Wnt1/frizzled-1/β-catenin tone that critically contributes to the survival and protection of adult midbrain DAergic neurons, with potential implications for drug design or drug action in PD. The dynamic interplay between astrocyte-derived factors and neurogenic signals in MPTP-induced nigrostriatal DAergic neurotoxicity and repair will be summarized, together with recent findings showing a critical role of glia-neural stem/progenitor cell (NPC) interactions aimed at overcoming neurodegeneration and inducing neurorestoration. Understanding the intrinsic plasticity of nigrostriatal DAergic neurons and deciphering the signals facilitating the crosstalk between astrocytes, microglia, DAergic neurons and NPCs may have major implications for the role of stem cell technology in PD, and for identifying potential therapeutic targets to induce endogenous neurorepair.

Roles of vitamin D in amyotrophic lateral sclerosis: possible genetic and cellular signaling mechanisms

Evidence suggests that there are aberrations in the vitamin D-endocrine system in subjects with amyotrophic lateral sclerosis (ALS). Here, we review the relationship between vitamin D and ALS. Vitamin D deficiency was reported in patients with ALS. Dietary vitamin D₃ supplementation improves functional capacity in the G93A transgenic mouse model of ALS. Genetic studies have provided an opportunity to identify the proteins that link vitamin D to ALS pathology, including major histocompatibility complex (MHC) class II molecules, toll-like receptors, poly(ADP-ribose) polymerase-1, heme oxygenase-1, and calcium-binding proteins, as well as the reduced form of nicotinamide adenine dinucleotide phosphate. Vitamin D also exerts its effect on ALS through cell-signaling mechanisms, including glutamate, matrix metalloproteinases, mitogen-activated protein kinase pathways, the Wnt/β-catenin signaling pathway, prostaglandins, reactive oxygen species, and nitric oxide synthase.

In conclusion, vitamin D may have a role in ALS. Further investigation of vitamin D in ALS patients is needed.

Peroxisome proliferator-activated receptors and Alzheimer's disease: hitting the blood-brain barrier

The blood-brain barrier (BBB) is often affected in several neurodegenerative disorders, such as Alzheimer's disease (AD). Integrity and proper functionality of the neurovascular unit are recognized to be critical for maintenance of the BBB. Research has traditionally focused on structural integrity more than functionality, and BBB alteration has usually been explained more as a consequence than a cause. However, ongoing evidence suggests that at the early stages, the BBB of a diseased brain often shows distinct expression patterns of specific carriers such as members of the ATP-binding cassette (ABC) transport protein family, which alter BBB traffic. In AD, amyloid-β (Aβ) deposits are a pathological hallmark and, as recently highlighted by Cramer et al. (2012), Aβ clearance is quite fundamental and is a less studied approach. Current knowledge suggests that BBB traffic plays a more important role than previously believed and that pharmacological modulation of the BBB may offer new therapeutic alternatives for AD. Recent investigations carried out in our laboratory indicate that peroxisome proliferator-activated receptor (PPAR) agonists are able to prevent Aβ-induced neurotoxicity in hippocampal neurons and cognitive impairment in a double transgenic mouse model of AD. However, even when enough literature about PPAR agonists and neurodegenerative disorders is available, the problem of how they exert their functions and help to prevent and rescue Aβ-induced neurotoxicity is poorly understood. In this review, along with highlighting the main features of the BBB and its role in AD, we will discuss information regarding the modulation of BBB components, including the possible role of PPAR agonists as BBB traffic modulators.

Wnt your brain be inflamed? Yes, it Wnt!

The roles of Wnts in neural development, synaptogenesis, and cancer are generally well characterized. Nonetheless, evidence exists that interactions between the immune and nervous systems control major brain regenerative processes ranging from physiological or pathological (reparative) regeneration to neurogenesis and synaptic plasticity. Recent studies describe deregulated Wnt-Fzd signaling in degenerative and inflammatory central nervous system (CNS) disorders, and the expression of Wnt signaling components in the immune system, and in immune-like cells of the mammalian CNS. This would suggest a likely involvement of Wnts in inflammation-driven brain damage and inflammation-directed brain repair. Here, we review how Wnts modulate neuroimmune interactions and offer a perspective on the most challenging therapeutic opportunities for those CNS diseases where injury-reactive Wnt-flavored inflammation precedes secondary neurodegeneration.

Spatio-temporal expression pattern of frizzled receptors after contusive spinal cord injury in adult rats

Background

Wnt proteins are a large family of molecules that are critically involved in multiple central nervous system (CNS) developmental processes. Experimental evidences suggest a role for this family of proteins in many CNS disorders, including spinal cord injury (SCI), which is a major neuropathology owing to its high prevalence and chronic sensorimotor functional sequelae. Interestingly, most Wnt proteins and their inhibitors are expressed in the uninjured spinal cord, and their temporal expression patterns are dramatically altered after injury. However, little is known regarding the expression of their better-known receptors, the Frizzled family, after SCI. Thus, the aim of the present study was to evaluate the expression of Frizzled receptors in the damaged spinal cord.

Findings

Based on the evidence that Wnts are expressed in the spinal cord and are transcriptionally regulated by SCI in adulthood, we analysed the spatio-temporal mRNA and protein expression patterns of Frizzled receptors after contusive SCI using quantitative RT-PCR and single and double immunohistochemistry, respectively. Our results show that almost all of the 10 known Frizzled receptors were expressed in specific spatial patterns in the uninjured spinal cords. Moreover, the Frizzled mRNAs and proteins were expressed after SCI, although their expression patterns were altered during the temporal progression of SCI. Finally, analysis of cellular Frizzled 5 expression pattern by double immunohistochemistry showed that, in the uninjured spinal cord, this receptor was expressed in neurons, oligodendrocytes, astrocytes, microglia and NG2⁺ glial precursors. After injury, Frizzled 5 was not only still expressed in oligodendrocytes, astrocytes and NG2⁺ glial precursors but also in axons at all evaluated time points. Moreover, Frizzled 5 was expressed in reactive microglia/macrophages from 3 to 14 days post-injury.

Conclusions

Our data suggest the involvement of Frizzled receptors in physiological spinal cord function and in the cellular and molecular events that characterise its neuropathology.

Wnt signaling: role in Alzheimer disease and schizophrenia

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

Tip60 HAT activity mediates APP induced lethality and apoptotic cell death in the CNS of a Drosophila Alzheimer's disease model

Histone acetylation of chromatin promotes dynamic transcriptional responses in neurons that influence neuroplasticity critical for cognitive ability. It has been demonstrated that Tip60 histone acetyltransferase (HAT) activity is involved in the transcriptional regulation of genes enriched for neuronal function as well as the control of synaptic plasticity. Accordingly, Tip60 has been implicated in the neurodegenerative disorder Alzheimer's disease (AD) via transcriptional regulatory complex formation with the AD linked amyloid precursor protein (APP) intracellular domain (AICD). As such, inappropriate complex formation may contribute to AD-linked neurodegeneration by misregulation of target genes involved in neurogenesis; however, a direct and causative epigenetic based role for Tip60 HAT activity in this process during neuronal development in vivo remains unclear. Here, we demonstrate that nervous system specific loss of Tip60 HAT activity enhances APP mediated lethality and neuronal apoptotic cell death in the central nervous system (CNS) of a transgenic AD fly model while remarkably, overexpression of Tip60 diminishes these defects. Notably, all of these effects are dependent upon the C-terminus of APP that is required for transcriptional regulatory complex formation with Tip60. Importantly, we show that the expression of certain AD linked Tip60 gene targets critical for regulating apoptotic pathways are modified in the presence of APP. Our results are the first to demonstrate a functional interaction between Tip60 and APP in mediating nervous system development and apoptotic neuronal cell death in the CNS of an AD fly model in vivo, and support a novel neuroprotective role for Tip60 HAT activity in AD neurodegenerative pathology.

Genome-wide analysis of a Wnt1-regulated transcriptional network implicates neurodegenerative pathways

Wnt proteins are critical to mammalian brain development and function. The canonical Wnt signaling pathway involves the stabilization and nuclear translocation of β-catenin; however, Wnt also signals through alternative, noncanonical pathways. To gain a systems-level, genome-wide view of Wnt signaling, we analyzed Wnt1-stimulated changes in gene expression by transcriptional microarray analysis in cultured human neural progenitor (hNP) cells at multiple time points over a 72-hour time course. We observed a widespread oscillatory-like pattern of changes in gene expression, involving components of both the canonical and the noncanonical Wnt signaling pathways. A higher-order, systems-level analysis that combined independent component analysis, waveform analysis, and mutual information-based network construction revealed effects on pathways related to cell death and neurodegenerative disease. Wnt effectors were tightly clustered with presenilin1 (PSEN1) and granulin (GRN), which cause dominantly inherited forms of Alzheimer's disease and frontotemporal dementia (FTD), respectively. We further explored a potential link between Wnt1 and GRN and found that Wnt1 decreased GRN expression by hNPs. Conversely, GRN knockdown increased WNT1 expression, demonstrating that Wnt and GRN reciprocally regulate each other. Finally, we provided in vivo validation of the in vitro findings by analyzing gene expression data from individuals with FTD. These unbiased and genome-wide analyses provide evidence for a connection between Wnt signaling and the transcriptional regulation of neurodegenerative disease genes.

How do they do Wnt they do?: regulation of transcription by the Wnt/β-catenin pathway

Wnt/β-catenin signalling is known to play many roles in metazoan development and tissue homeostasis. Misregulation of the pathway has also been linked to many human diseases. In this review, specific aspects of the pathway's involvement in these processes are discussed, with an emphasis on how Wnt/β-catenin signalling regulates gene expression in a cell and temporally specific manner. The T-cell factor (TCF) family of transcription factors, which mediate a large portion of Wnt/β-catenin signalling, will be discussed in detail. Invertebrates contain a single TCF gene that contains two DNA-binding domains, the high mobility group (HMG) domain and the C-clamp, which increases the specificity of DNA binding. In vertebrates, the situation is more complex, with four TCF genes producing many isoforms that contain the HMG domain, but only some of which possess a C-clamp. Vertebrate TCFs have been reported to act in concert with many other transcription factors, which may explain how they obtain sufficient specificity for specific DNA sequences, as well as how they achieve a wide diversity of transcriptional outputs in different cells.

Wnt/Ca2+ signaling pathway: a brief overview

The non-canonical Wnt/Ca(2+) signaling cascade is less characterized than their canonical counterpart, the Wnt/β-catenin pathway. The non-canonical Wnt signaling pathways are diverse, defined as planer cell polarity pathway, Wnt-RAP1 signaling pathway, Wnt-Ror2 signaling pathway, Wnt-PKA pathway, Wnt-GSK3MT pathway, Wnt-aPKC pathway, Wnt-RYK pathway, Wnt-mTOR pathway, and Wnt/calcium signaling pathway. All these pathways exhibit a considerable degree of overlap between them. The Wnt/Ca(2+) signaling pathway was deciphered as a crucial mediator in development. However, now there is substantial evidence that the signaling cascade is involved in many other molecular phenomena. Many aspects of Wnt/Ca(2+) pathway are yet enigmatic. This review will give a brief overview of the fundamental and evolving concepts of the Wnt/Ca(2+) signaling pathway.

Functional genomic analyses identify pathways dysregulated by progranulin deficiency, implicating Wnt signaling

Progranulin (GRN) mutations cause frontotemporal dementia (FTD), but GRN's function in the CNS remains largely unknown. To identify the pathways downstream of GRN, we used weighted gene coexpression network analysis (WGCNA) to develop a systems-level view of transcriptional alterations in a human neural progenitor model of GRN-deficiency. This highlighted key pathways such as apoptosis and ubiquitination in GRN deficient human neurons, while revealing an unexpected major role for the Wnt signaling pathway, which was confirmed by analysis of gene expression data from postmortem FTD brain. Furthermore, we observed that the Wnt receptor Fzd2 was one of only a few genes upregulated at 6 weeks in a GRN knockout mouse, and that FZD2 reduction caused increased apoptosis, while its upregulation promoted neuronal survival in vitro. Together, these in vitro and in vivo data point to an adaptive role for altered Wnt signaling in GRN deficiency-mediated FTD, representing a potential therapeutic target.

A Wnt1 regulated Frizzled-1/β-Catenin signaling pathway as a candidate regulatory circuit controlling mesencephalic dopaminergic neuron-astrocyte crosstalk: Therapeutical relevance for neuron survival and neuroprotection

BACKGROUND

Dopamine-synthesizing (dopaminergic, DA) neurons in the ventral midbrain (VM) constitute a pivotal neuronal population controlling motor behaviors, cognitive and affective brain functions, which generation critically relies on the activation of Wingless-type MMTV integration site (Wnt)/β-catenin pathway in their progenitors. In Parkinson's disease, DA cell bodies within the substantia nigra pars compacta (SNpc) progressively degenerate, with causes and mechanisms poorly understood. Emerging evidence suggests that Wnt signaling via Frizzled (Fzd) receptors may play a role in different degenerative states, but little is known about Wnt signaling in the adult midbrain. Using in vitro and in vivo model systems of DA degeneration, along with functional studies in both intact and SN lesioned mice, we herein highlight an intrinsic Wnt1/Fzd-1/β-catenin tone critically contributing to the survival and protection of adult midbrain DA neurons.

RESULTS

In vitro experiments identifie Fzd-1 receptor expression at a mRNA and protein levels in dopamine transporter (DAT) expressing neurons, and demonstrate the ability of exogenous Wnt1 to exert robust neuroprotective effects against Caspase-3 activation, the loss of tyrosine hydroxylase-positive (TH+) neurons and [3H] dopamine uptake induced by different DA-specific insults, including serum and growth factor deprivation, 6-hydroxydopamine and MPTP/MPP+. Co-culture of DA neurons with midbrain astrocytes phenocopies Wnt1 neuroprotective effects, whereas RNA interference-mediated knockdown of Wnt1 in midbrain astrocytes markedly reduces astrocyte-induced TH+ neuroprotection. Likewise, silencing β-catenin mRNA or knocking down Fzd-1 receptor expression in mesencephalic neurons counteract astrocyte-induced TH+ neuroprotection. In vivo experiments document Fzd-1 co-localization with TH+ neurons within the intact SNpc and blockade of Fzd/β-catenin signaling by unilateral infusion of a Fzd/β-catenin antagonist within the SN induces reactive astrocytosis and acutely inhibits TH+ neuron survival in ipsilateral SNpc, an effect efficiently prevented by pharmacological activation of β-catenin signaling within the SNpc.

CONCLUSION

These results defining a novel Wnt1/Fzd-1/β-catenin astrocyte-DA autoprotective loop provide a new mechanistic inside into the regulation of pro-survival processes, with potentially relevant consequences for drug design or drug action in Parkinson's disease.

Tetrahydrohyperforin prevents cognitive deficit, Aβ deposition, tau phosphorylation and synaptotoxicity in the APPswe/PSEN1ΔE9 model of Alzheimer's disease: a possible effect on APP processing

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive deterioration of cognitive abilities, amyloid-β peptide (Aβ) accumulation and synaptic alterations. Previous studies indicated that hyperforin, a component of the St John's Wort, prevents Aβ neurotoxicity and some behavioral impairments in a rat model of AD. In this study we examined the ability of tetrahydrohyperforin (IDN5607), a stable hyperforin derivative, to prevent the cognitive deficit and synaptic impairment in an in vivo model of AD. In double transgenic APPswe/PSEN1ΔE9 mice, IDN5706 improves memory and prevents the impairment of synaptic plasticity in a dose-dependent manner, inducing a recovery of long-term potentiation. In agreement with these findings, IDN5706 prevented the decrease in synaptic proteins in hippocampus and cortex. In addition, decreased levels of tau hyperphosphorylation, astrogliosis, and total fibrillar and oligomeric forms of Aβ were determined in double transgenic mice treated with IDN5706. In cultured cells, IDN5706 decreased the proteolytic processing of the amyloid precursor protein that leads to Aβ peptide generation. These findings indicate that IDN5706 ameliorates AD neuropathology and could be considered of therapeutic relevance in AD treatment.

Role of β-catenin/TCF-4 signaling in HIV replication and pathogenesis: insights to informing novel anti-HIV molecular therapeutics

A greater understanding of the interaction between HIV and host signaling pathways that restrict virus production may lead to new methods to purge virus from latent reservoirs and enhance survival/function of cells targeted by HIV. This review highlights the role of the Wnt/β-catenin pathway as a host factor that represses HIV replication in multiple targets, especially those relevant to HIV in the central nervous system.

Huperzine A activates Wnt/β-catenin signaling and enhances the nonamyloidogenic pathway in an Alzheimer transgenic mouse model

Huperzine A (HupA) is a reversible and selective inhibitor of acetylcholinesterase (AChE), and it has multiple targets when used for Alzheimer's disease (AD) therapy. In this study, we searched for new mechanisms by which HupA could activate Wnt signaling and reduce amyloidosis in AD brain. A nasal gel containing HupA was prepared. No obvious toxicity of intranasal administration of HupA was found in mice. HupA was administered intranasally to β-amyloid (Aβ) precursor protein and presenilin-1 double-transgenic mice for 4 months. We observed an increase in ADAM10 and a decrease in BACE1 and APP695 protein levels and, subsequently, a reduction in Aβ levels and Aβ burden were present in HupA-treated mouse brain, suggesting that HupA enhances the nonamyloidogenic APP cleavage pathway. Importantly, our results further showed that HupA inhibited GSK3α/β activity, and enhanced the β-catenin level in the transgenic mouse brain and in SH-SY5Y cells overexpressing Swedish mutation APP, suggesting that the neuroprotective effect of HupA is not related simply to its AChE inhibition and antioxidation, but also involves other mechanisms, including targeting of the Wnt/β-catenin signaling pathway in AD brain.

Amyloid-β triggers the release of neuronal hexokinase 1 from mitochondria

Brain accumulation of the amyloid-β peptide (Aβ) and oxidative stress underlie neuronal dysfunction and memory loss in Alzheimer's disease (AD). Hexokinase (HK), a key glycolytic enzyme, plays important pro-survival roles, reducing mitochondrial reactive oxygen species (ROS) generation and preventing apoptosis in neurons and other cell types. Brain isozyme HKI is mainly associated with mitochondria and HK release from mitochondria causes a significant decrease in enzyme activity and triggers oxidative damage. We here investigated the relationship between Aβ-induced oxidative stress and HK activity. We found that Aβ triggered HKI detachment from mitochondria decreasing HKI activity in cortical neurons. Aβ oligomers further impair energy metabolism by decreasing neuronal ATP levels. Aβ-induced HKI cellular redistribution was accompanied by excessive ROS generation and neuronal death. 2-deoxyglucose blocked Aβ-induced oxidative stress and neuronal death. Results suggest that Aβ-induced cellular redistribution and inactivation of neuronal HKI play important roles in oxidative stress and neurodegeneration in AD.

Functional aspects of redox control during neuroinflammation

Neuroinflammation is a CNS reaction to injury in which some severe pathologies, regardless of their origin, converge. The phenomenon emphasizes crosstalk between neurons and glia and reveals a complex interaction with oxidizing agents through redox sensors localized in enzymes, receptors, and transcription factors. When oxidizing pressures cause reversible molecular changes, such as minimal or transitory proinflammatory cytokine overproduction, redox couples provide a means of translating the presence of reactive oxygen or nitrogen species into useful signals in the cell. Additionally, thiol-based redox sensors convey information about localized changes in redox potential induced by physiologic or pathologic situations. They are susceptible to oxidative changes and become key events during neuroinflammation, altering the course of a signaling response or the behavior of specific transcription factors. When oxidative stress augments the pressure on the intracellular environment, the effective reduction potential of redox pairs diminishes, and cell signaling shifts toward proinflammatory and proapoptotic signals, creating a vicious cycle between oxidative stress and neuroinflammation. In addition, electrophilic compounds derived from the oxidative cascade react with key protein thiols and interfere with redox signaling. This article reviews the relevant functional aspects of redox control during the neuroinflammatory process.

Genes associated with alcohol abuse and tobacco smoking in the human nucleus accumbens and ventral tegmental area

BACKGROUND

The incidence of alcohol and tobacco co-abuse is as high as 80%. The molecular mechanism underlying this comorbidity is virtually unknown, but interactions between these drugs have important implications for the development of and recovery from drug dependence.

METHODS

We investigated the effects of chronic tobacco and alcohol abuse and the interaction of the 2 behaviors on global gene expression in the human nucleus accumbens using cDNA microarrays and 20 alcoholic and control cases, with and without smoking comorbidity. Changes in gene expression were established by factorial ANOVA. Unsupervised hierarchical clustering was utilized to probe the strength of the data sets. Applying real-time PCR differential expression of candidate genes was confirmed in the nucleus accumbens and explored further in a second core region of the mesolimbic system, the ventral tegmental area.

RESULTS

Subjecting the data sets derived from microarray gene expression screening to unsupervised hierarchical clustering tied the cases into distinct groups. When considering all alcohol-responsive genes, alcoholics were separated from nonalcoholics with the exception of 1 control case. All smokers were distinguished from nonsmokers based on similarity in expression of smoking-sensitive genes. In the nucleus accumbens, alcohol-responsive genes were associated with transcription, lipid metabolism, and signaling. Smoking-sensitive genes were predominantly assigned to functional groups concerned with RNA processing and the endoplasmic reticulum. Both drugs influenced the expression of genes involved in matrix remodeling, proliferation, and cell morphogenesis. Additionally, a gene set encoding proteins involved in the canonical pathway "regulation of the actin cytoskeleton" was induced in response to alcohol and tobacco co-abuse and included. Alcohol abuse elevated the expression of candidate genes in this pathway in the nucleus accumbens and ventral tegmental area, while smoking comorbidity blunted this induction in the ventral tegmental area.

CONCLUSIONS

The region-specific modulation of alcohol-sensitive gene expression by smoking may have important consequences for alcohol-induced aberrations within the mesolimbic dopaminergic system.

Wnt signaling modulates pre- and postsynaptic maturation: therapeutic considerations

Wnt signaling regulates a wealth of aspects of nervous system development and function in embryonic stages and in adulthood. The expression of Wnt ligands and components of the Wnt signaling machinery in early stages of neural development has been related to its role in neurite patterning and in synaptogenesis. Moreover, its expression in the mature nervous system suggests a role for this pathway in synaptic maintenance and function. Therefore, it is of crucial relevance the understanding of the mechanisms by which Wnt signaling regulates these processes. Herein, we discuss how different Wnt ligands, acting through different Wnt signaling pathways, operate in pre- and postsynaptic regions to modulate synapse structure and function. We also elaborate on the idea that Wnt signaling pathways are a target for the treatment of neurodegenerative diseases that affect synaptic integrity, such as Alzheimer's disease.

Activation of Wnt signaling by lithium and rosiglitazone reduced spatial memory impairment and neurodegeneration in brains of an APPswe/PSEN1DeltaE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive deterioration of cognitive abilities, accumulation of the amyloid-beta-peptide (Abeta) and synaptic alterations. Treatment with lithium has been shown to provide neuroprotection against several insults, including protection against Abeta neurotoxicity in vitro. Rosiglitazone, a peroxisome proliferator activated receptor-gamma agonist, has been shown to attenuate Abeta-peptide neurotoxic effects, including the inflammatory response of microglia and astrocytes. Both types of drugs activate Wnt signaling, a pathway that has been shown to be related to AD. In this study, a double transgenic mouse model, which coexpresses APPswe and the exon 9 deletion of the presenilin 1 (PSEN1) gene, was used to examine, in vivo, the effect of lithium and rosiglitazone on Abeta neurotoxicity. Mice were tested for spatial memory, and their brain samples were used for histochemical and biochemical analysis. In this study, we report that both drugs significantly reduced (1) spatial memory impairment induced by amyloid burden; (2) Abeta aggregates and Abeta oligomers; and (3) astrocytic and microglia activation. They also prevented changes in presynaptic and postsynaptic marker proteins. Finally, both drugs activate Wnt signaling shown by the increase in beta-catenin and by the inhibition of the glycogen synthase kinase-3beta. We conclude that lithium and rosiglitazone, possibly by the activation of the Wnt signaling pathway, reduce various AD neuropathological markers and may be considered as potential therapeutic agents against the disease.

Wnt-5a occludes Abeta oligomer-induced depression of glutamatergic transmission in hippocampal neurons

Background

Soluble amyloid-β (Aβ;) oligomers have been recognized to be early and key intermediates in Alzheimer's disease (AD)-related synaptic dysfunction. Aβ oligomers block hippocampal long-term potentiation (LTP) and impair rodent spatial memory. Wnt signaling plays an important role in neural development, including synaptic differentiation.

Results

We report here that the Wnt signaling activation prevents the synaptic damage triggered by Aβ oligomers. Electrophysiological analysis of Schaffer collaterals-CA1 glutamatergic synaptic transmission in hippocampal slices indicates that Wnt-5a increases the amplitude of field excitatory postsynaptic potentials (fEPSP) and both AMPA and NMDA components of the excitatory postsynaptic currents (EPSCs), without modifying the paired pulse facilitation (PPF). Conversely, in the presence of Aβ oligomers the fEPSP and EPSCs amplitude decreased without modification of the PPF, while the postsynaptic scaffold protein (PSD-95) decreased as well. Co-perfusion of hippocampal slices with Wnt-5a and Aβ oligomers occludes against the synaptic depression of EPSCs as well as the reduction of PSD-95 clusters induced by Aβ oligomers in neuronal cultures. Taken together these results indicate that Wnt-5a and Aβ oligomers inversely modulate postsynaptic components.

Conclusion

These results indicate that post-synaptic damage induced by Aβ oligomers in hippocampal neurons is prevented by non-canonical Wnt pathway activation.