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

Ferrosenescence: The iron age of neurodegeneration?

Aging has been associated with iron retention in many cell types, including the neurons, promoting neurodegeneration by ferroptosis. Excess intracellular iron accelerates aging by damaging the DNA and blocking genomic repair systems, a process we define as ferrosenescence. Novel neuroimaging and proteomic techniques have pinpointed indicators of both iron retention and ferrosenescence, allowing for their early correction, potentially bringing prevention of neurodegenerative disorders within reach. In this review, we take a closer look at the early markers of iron dyshomeostasis in neurodegenerative disorders, focusing on preventive strategies based on nutritional and microbiome manipulations.

BACE1 inhibition by microdose lithium formulation NP03 rescues memory loss and early stage amyloid neuropathology

Lithium is first-line therapy for bipolar affective disorder and has recently been shown to have protective effects in populations at risk for Alzheimer's disease (AD). However, the mechanism underlying this protection is poorly understood and consequently limits its possible therapeutic application in AD. Moreover, conventional lithium formulations have a narrow therapeutic window and are associated with a severe side effect profile. Here we evaluated a novel microdose formulation of lithium, coded NP03, in a well-characterized rat model of progressive AD-like amyloid pathology. This formulation allows microdose lithium delivery to the brain in the absence of negative side effects. We found that NP03 rescued key initiating components of AD pathology, including inactivating GSK-3β, reducing BACE1 expression and activity, and reducing amyloid levels. Notably, NP03 rescued memory loss, impaired CRTC1 promoter binding of synaptic plasticity genes and hippocampal neurogenesis. These results raise the possibility that NP03 be of therapeutic value in the early or preclinical stages of AD.

Lithium alleviates neurotoxic prion peptide-induced synaptic damage and neuronal death partially by the upregulation of nuclear target REST and the restoration of Wnt signaling

Prion diseases are a group of infectious neurodegenerative diseases characterized by multiple neuropathological hallmarks, including accumulation of PrP^Sc, synaptic damage, and neuronal death. We previously reported that the repressor element 1-silencing transcription factor (REST), a novel neuroprotective marker in neurodegeneration, protects neurons against neurotoxic peptide (PrP106-126)-induced neurotoxicity, but fails to maintain survival following prolonged exposure to PrP106-126. Because Wnt signaling partially induces REST and is activated by lithium, we investigated the effects of lithium on REST in prion diseases. Lithium restores nuclear expression of REST, which is essential for regulating survival proteins. Lithium also mimics neuroprotective functions when REST is blocked, and these beneficial effects are additive with REST overexpression under physiological conditions. Reciprocally, under PrP106-126-stimulated pathological conditions, REST plays a critical role in the neuroprotective mechanisms of lithium treatment. Although lithium recovers Wnt signaling by inhibiting glycogen synthase kinase-3β and stabilizing β-catenin, restores survival associated proteins after exposure to PrP106-126 in primary cortical neurons. Knockdown of REST significantly suppresses the neuroprotective function of lithium. Conversely, overexpression of REST partially recovers its actions. Notably, lithium directly alleviates PrP106-126-induced synaptic damage and neuronal cell death by preventing changes in presynaptic and postsynaptic marker proteins and promoting survival pathways also partially via the expression of REST. Our results suggest that REST acts as a novel and important nuclear target for lithium. We hypothesize that PrP106-126-stimulated neurotoxicity induces Wnt signaling dysfunction and lithium mimics this signaling cascade, suggesting that lithium should be considered as a potential therapeutic agent against prion diseases.

Metabolic Syndrome as a Risk Factor for Alzheimer's Disease: Is Aβ a Crucial Factor in Both Pathologies?

SIGNIFICANCE

Recently, chronic degenerative diseases have become one of the main health problems worldwide. That is the case of Alzheimer's disease (AD) and metabolic syndrome (MetS), whose expression can be influenced by different risk factors. Recent Advances: In recent decades, it has been widely described that MetS increases the risk of cognitive impairment and dementia. MetS pathogenesis involves several vascular risk factors such as diabetes, dyslipidemia, hypertension, and insulin resistance (I/R).

CRITICAL ISSUES

Reported evidence shows that vascular risk factors are associated with AD, particularly in the development of protein aggregation, inflammation, oxidative stress, neuronal dysfunction, and disturbances in signaling pathways, with insulin receptor signaling being a common alteration between MetS and AD.

FUTURE DIRECTIONS

Insulin signaling has been involved in tau phosphorylation and amyloid β (Aβ) metabolism. However, it has also been demonstrated that Aβ oligomers can bind to insulin receptors, triggering their internalization, decreasing neuron responsiveness to insulin, and promoting insulin I/R. Thus, it could be argued that Aβ could be a convergent factor in the development of both pathologies. Antioxid. Redox Signal. 26, 542-560.

Therapeutic potential of nuclear receptor agonists in Alzheimer's disease

Alzheimer's disease (AD) is characterized by an extensive accumulation of amyloid-β (Aβ) peptide, which triggers a set of deleterious processes, including synaptic dysfunction, inflammation, and neuronal injury, leading to neuronal loss and cognitive impairment. A large body of evidence supports that nuclear receptor (NR) activation could be a promising therapeutic approach for AD. NRs are ligand-activated transcription factors that regulate gene expression and have cell type-specific effects. In this review, we discuss the mechanisms that underlie the beneficial effects of NRs in AD. Moreover, we summarize studies reported in the last 10-15 years and their major outcomes arising from the pharmacological targeting of NRs in AD animal models. The dissection of the pathways regulated by NRs in the context of AD is of importance in identifying novel and effective therapeutic strategies.

Lithium suppression of tau induces brain iron accumulation and neurodegeneration

Lithium is a first-line therapy for bipolar affective disorder. However, various adverse effects, including a Parkinson-like hand tremor, often limit its use. The understanding of the neurobiological basis of these side effects is still very limited. Nigral iron elevation is also a feature of Parkinsonian degeneration that may be related to soluble tau reduction. We found that magnetic resonance imaging T₂ relaxation time changes in subjects commenced on lithium therapy were consistent with iron elevation. In mice, lithium treatment lowers brain tau levels and increases nigral and cortical iron elevation that is closely associated with neurodegeneration, cognitive loss and parkinsonian features. In neuronal cultures lithium attenuates iron efflux by lowering tau protein that traffics amyloid precursor protein to facilitate iron efflux. Thus, tau- and amyloid protein precursor-knockout mice were protected against lithium-induced iron elevation and neurotoxicity. These findings challenge the appropriateness of lithium as a potential treatment for disorders where brain iron is elevated (for example, Alzheimer's disease), and may explain lithium-associated motor symptoms in susceptible patients.

Altered Wnt Signaling Pathway in Cognitive Impairment Caused by Chronic Intermittent Hypoxia: Focus on Glycogen Synthase Kinase-3β and β-catenin

BACKGROUND

Cognitive impairment is a severe complication caused by obstructive sleep apnea (OSA). The mechanisms of causation are still unclear. The Wnt/β-catenin signaling pathway is involved in cognition, and abnormalities in it are implicated in neurological disorders. Here, we explored the Wnt/β-catenin signaling pathway abnormalities caused by chronic intermittent hypoxia (CIH), the most characteristic pathophysiological component of OSA.

METHODS

We divided 32 4-week-old male C57/BL mice into four groups of eight each: a CIH + normal saline (NS) group, CIH + LiCl group, sham CIH + NS group, and a sham CIH + LiCl group. The spatial learning performance of each group was assessed by using the Morris water maze (MWM). Protein expressions of glycogen synthase kinase-3β (GSK-3β) and β-catenin in the hippocampus were examined using the Western blotting test. EdU labeling and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining methods were used, respectively, to determine the proliferation and apoptosis of neurons in the hippocampal dentate gyrus region.

RESULTS

Mice exposed to CIH showed impaired spatial learning performance in the MWM, including increased mean escape latencies to reach the target platform, decreased mean times passing through the target platform and mean duration in the target quadrant. The GSK-3β activity increased, and expression of β-catenin decreased significantly in the hippocampus of the CIH-exposed mice. Besides, CIH significantly increased hippocampal neuronal apoptosis, with an elevated apoptosis index. Meanwhile, LiCl decreased the activity of GSK-3β and increased the expression of β-catenin and partially reversed the spatial memory deficits in MWM and the apoptosis caused by CIH.

CONCLUSIONS

Wnt/β-catenin signaling pathway abnormalities possibly play an important role in the development of cognitive deficits among mice exposed to CIH and that LiCl might attenuate CIH-induced cognitive impairment via Wnt/β-catenin signaling pathway.

Acute stress enhances the expression of neuroprotection- and neurogenesis-associated genes in the hippocampus of a mouse restraint model

Stress arises from an external demand placed on an organism that triggers physiological, cognitive and behavioural responses in order to cope with that request. It is thus an adaptive response useful for the survival of an organism. The objective of this study was to identify and characterize global changes in gene expression in the hippocampus in response to acute stress stimuli, by employing a mouse model of short-term restraint stress. In our experimental design mice were subjected to a one time exposure of restraint stress and the regulation of gene expression in the hippocampus was examined 3, 12 and 24 hours thereafter. Microarray analysis revealed that mice which had undergone acute restraint stress differed from non-stressed controls in global hippocampal transcriptional responses. An up-regulation of transcripts contributing directly or indirectly to neurogenesis and neuronal protection including, Ttr, Rab6, Gh, Prl, Ndufb9 and Ndufa6, was observed. Systems level analyses revealed a significant enrichment for neurogenesis, neuron morphogenesis- and cognitive functions-related biological process terms and pathways. This work further supports the hypothesis that acute stress mediates a positive action on the hippocampus favouring the formation and the preservation of neurons, which will be discussed in the context of current data from the literature.

Wnt Signaling Prevents the Aβ Oligomer-Induced Mitochondrial Permeability Transition Pore Opening Preserving Mitochondrial Structure in Hippocampal Neurons

Alzheimer's disease (AD) is a neurodegenerative disorder mainly known for synaptic impairment and neuronal cell loss, affecting memory processes. Beside these damages, mitochondria have been implicated in the pathogenesis of AD through the induction of the mitochondrial permeability transition pore (mPTP). The mPTP is a non-selective pore that is formed under apoptotic conditions, disturbing mitochondrial structure and thus, neuronal viability. In AD, Aβ oligomers (Aβos) favor the opening of the pore, activating mitochondria-dependent neuronal cell death cascades. The Wnt signaling activated through the ligand Wnt3a has been described as a neuroprotective signaling pathway against amyloid-β (Aβ) peptide toxicity in AD. However, the mechanisms by which Wnt signaling prevents Aβos-induced neuronal cell death are unclear. We proposed here to study whether Wnt signaling protects neurons earlier than the late damages in the progression of the disease, through the preservation of the mitochondrial structure by the mPTP inhibition. To study specific events related to mitochondrial permeabilization we performed live-cell imaging from primary rat hippocampal neurons, and electron microscopy to analyze the mitochondrial morphology and structure. We report here that Wnt3a prevents an Aβos-induced cascade of mitochondrial events that leads to neuronal cell death. This cascade involves (a) mPTP opening, (b) mitochondrial swelling, (c) mitochondrial membrane potential loss and (d) cytochrome c release, thus leading to neuronal cell death. Furthermore, our results suggest that the activation of the Wnt signaling prevents mPTP opening by two possible mechanisms, which involve the inhibition of mitochondrial GSK-3β and/or the modulation of mitochondrial hexokinase II levels and activity. This study suggests a possible new approach for the treatment of AD from a mitochondrial perspective, and will also open new lines of study in the field of Wnt signaling in neuroprotection.

Combination treatment with leptin and pioglitazone in a mouse model of Alzheimer's disease

INTRODUCTION

Combination therapy approaches may be necessary to address the many facets of pathologic change in the brain in Alzheimer's disease (AD). The drugs leptin and pioglitazone have previously been shown individually to have neuroprotective and anti-inflammatory actions, respectively, in animal models.

METHODS

We studied the impact of combined leptin and pioglitazone treatment in 6-month-old APP/PS1 (APPswe/PSEN1dE9) transgenic AD mouse model.

RESULTS

We report that an acute 2-week treatment with combined leptin and pioglitazone resulted in a reduction of spatial memory deficits (Y maze) and brain β-amyloid levels (soluble β-amyloid and amyloid plaque burden) relative to vehicle-treated animals. Combination treatment was also associated with amelioration in plaque-associated neuritic pathology and synapse loss, and also a significantly reduced neocortical glial response.

DISCUSSION

Combination therapy with leptin and pioglitazone ameliorates pathologic changes in APP/PS1 mice and may represent a potential treatment approach for AD.

PPARγ as a therapeutic target to rescue mitochondrial function in neurological disease

There is increasing evidence for the involvement of mitochondrial dysfunction and oxidative stress in the pathogenesis of many of the major neurodegenerative and neuroinflammatory diseases, suggesting that mitochondrial and antioxidant pathways may represent potential novel therapeutic targets. Recent years have seen a rapidly growing interest in the use of therapeutic strategies that can limit the defects in, or even to restore, mitochondrial function while reducing free radical generation. The peroxisome proliferation-activated receptor gamma (PPARγ), a ligand-activated transcription factor, has a wide spectrum of biological functions, regulating mitochondrial function, mitochondrial turnover, energy metabolism, antioxidant defence and redox balance, immune responses and fatty acid oxidation. In this review, we explore the evidence for potential beneficial effects of PPARγ agonists in a number of neurological disorders, including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington's disease, ischaemia, autoimmune encephalomyelitis and neuropathic pain. We discuss the mechanisms underlying those beneficial effects in particular in relation to mitochondrial function, antioxidant defence, cell death and inflammation, and suggest that the PPARγ agonists show significant promise as therapeutic agents in otherwise intractable neurological disease.

Molecular Signatures of Psychosocial Stress and Cognition Are Modulated by Chronic Lithium Treatment

Chronic psychosocial stress is an important environmental risk factor of psychiatric diseases such as schizophrenia. Social defeat in rodents has been shown to be associated with maladaptive cellular and behavioral consequences including cognitive impairments. Although gene expression changes upon psychosocial stress have been described, a comprehensive transcriptome profiling study at the global level in precisely defined hippocampal subregions which are associated with learning has been lacking. In this study, we exposed adult C57Bl/6N mice for 3 weeks to "resident-intruder" paradigm and combined laser capture microdissection with microarray analyses to identify transcriptomic signatures of chronic psychosocial stress in dentate gyrus and CA3 subregion of the dorsal hippocampus. At the individual transcript level, we detected subregion specific stress responses whereas gene set enrichment analyses (GSEA) identified several common pathways upregulated upon chronic psychosocial stress related to proteasomal function and energy supply. Behavioral profiling revealed stress-associated impairments most prominent in fear memory formation which was prevented by chronic lithium treatment. Thus, we again microdissected the CA3 region and performed global transcriptome analysis to search for molecular signatures altered by lithium treatment in stressed animals. By combining GSEA with unsupervised clustering, we detected pathways that are regulated by stress and lithium in the CA3 region of the hippocampus including proteasomal components, oxidative phosphorylation, and anti-oxidative mechanisms. Our study thus provides insight into hidden molecular phenotypes of chronic psychosocial stress and lithium treatment and proves a beneficial role for lithium treatment as an agent attenuating negative effects of psychosocial stress on cognition.

The role of the Wnt canonical signaling in neurodegenerative diseases

The Wnt/β-catenin or Wnt canonical pathway controls multiple biological processes throughout development and adult life. Growing evidences have suggested that deregulation of the Wnt canonical pathway could be involved in the pathogenesis of neurodegenerative diseases. The Wnt canonical signaling is a pathway tightly regulated, which activation results in the inhibition of the Glycogen Synthase Kinase 3β (GSK-3β) function and in increased β-catenin activity, that migrates into the nucleus, activating the transcription of the Wnt target genes. Conversely, when the Wnt canonical pathway is turned off, increased levels of GSK-3β promote β-catenin degradation. Hence, GSK-3β could be considered as a key regulator of the Wnt canonical pathway. Of note, GSK-3β has also been involved in the modulation of inflammation and apoptosis, determining the delicate balance between immune tolerance/inflammation and neuronal survival/neurodegeneration. In this review, we have summarized the current acknowledgements about the role of the Wnt canonical pathway in the pathogenesis of some neurodegenerative diseases including Alzheimer's disease, cerebral ischemia, Parkinson's disease, Huntington's disease, multiple sclerosis and amyotrophic lateral sclerosis, with particular regard to the main in vitro and in vivo studies in this field, by reviewing 85 research articles about.

Enhancing Beta-Catenin Activity via GSK3beta Inhibition Protects PC12 Cells against Rotenone Toxicity through Nurr1 Induction

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic (DA) neurons in the substantial nigra pars compacta. Increasing evidence showed that Wnt/β-catenin pathway and the orphan nuclear receptor Nurr1 play crucial roles in the survival and functional maintenance of DA neurons in the midbrain and GSK-3β antagonists LiCl and SB216763 were used to activate Wnt/β-catenin pathway experimentally. However, the detail mechanism underlying the neuroprotection against apoptosis on DA neuron is still unclear and the interaction between Wnt/β-catenin and Nurr1 remains undisclosed. In this study, using cell biological assay we investigated the function of Wnt/β-catenin and its crosstalk with Nurr1 on the course of PC12 cell degeneration in vitro. Our data showed that PC12 cell viability was inhibited by rotenone, but attenuated by GSK-3β antagonists LiCl or SB216763. The activity of Wnt/β-catenin pathway was deregulated on exposure of rotenone in a concentration-dependent manner. After the interference of β-catenin with siRNA, LiCl or SB216763 failed to protect PC12 cells from apoptosis by the rotenone toxicity. Our data confirmed that Wnt/β-catenin signaling activated by LiCl or SB216763 enhanced Nurr1 expression to 2.75 ± 0.55 and 4.06 ± 0.41 folds respectively compared with control detected by real-time PCR and the interaction of β-catenin with Nurr1 was identified by co-immunoprecipitate analysis. In conclusion, the data suggested that Wnt/β-catenin and Nurr1 are crucial factors in the survival of DA neurons, and the activation of Wnt/β-catenin pathway exerts protective effects on DA neurons partly by mean of a co-active pattern with Nurr1. This finding may shed a light on the potential treatment of Parkinson disease.

On cognitive ecology and the environmental factors that promote Alzheimer disease: lessons from Octodon degus (Rodentia: Octodontidae)

Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.

Resveratrol Protects SAMP8 Brain Under Metabolic Stress: Focus on Mitochondrial Function and Wnt Pathway

Metabolic stress induced by high-fat (HF) diet leads to cognitive dysfunction and aging, but the physiological mechanisms are not fully understood. Senescence-accelerated prone mouse (SAMP8) models were conducted under metabolic stress conditions by feeding HF for 15 weeks, and the preventive effect of resveratrol was studied. This dietary strategy demonstrates cognitive impairment in SAMP8-HF and significant preventive effect by resveratrol-treated animals. Hippocampal changes in the proteins involved in mitochondrial dynamics optic atrophy-1 protein (OPA1) and mitofusin 2 (MFN2) comprised a differential feature found in SAMP8-HF that was prevented by resveratrol. Electronic microscopy showed a larger mitochondria in SAMP8-HF + resveratrol (SAMP8-HF + RV) than in SAMP8-HF, indicating increases in fusion processes in resveratrol-treated mice. According to the mitochondrial morphology, significant increases in the I-NDUFB8, II-SDNB, III-UQCRC2, and V-ATPase complexes, in addition to that of voltage-dependent anion channel 1 (VDAC1)/porin, were found in resveratrol-treated animals with regard to SAMP8-HF, reaching control-animal levels. Moreover, tumor necrosis factor alpha (TNF-α) and interleukin (IL-6) were increased after HF, and resveratrol prevents its increase. Moreover, we found that the HF diet affected the Wnt pathway, as demonstrated by β-catenin inactivation and modification in the expression of several components of this pathway. Resveratrol induced strong activation of β-catenin. The metabolic stress rendered in the cognitive and cellular pathways altered in SAMP8 focus on different targets in order to act on preventing cognitive impairment in neurodegeneration, and resveratrol can offer therapeutic possibilities for preventive strategies in aging or neurodegenerative conditions.

Neuroprotective Potential of Novel Multi-Targeted Isoalloxazine Derivatives in Rodent Models of Alzheimer's Disease Through Activation of Canonical Wnt/β-Catenin Signalling Pathway

Previous reports suggest that Alzheimer's disease is protected by cholinesterase inhibitors. We synthesized some isoalloxazine derivatives and evaluated them using in vitro cholinesterase inhibition assay. Two of the compounds (7m and 7q) were figured out as potent cholinesterase inhibitors. They further showed anti-Aβ aggregatory activity in the in vitro assay. The current study deals with the evaluation of neuroprotective potentials of the potent compounds (7m and 7q) using different in vitro and in vivo experiments. The compounds were first assessed for their tendency to cross blood-brain barrier using in vitro permeation assay. They were evaluated using scopolamine-induced amnesic mice model. Additionally, ROS scavenging and anti-apoptotic properties of 7m and 7q were established against Aβ1-42-induced toxicity in rat hippocampal neuronal cells. 7m and 7q were also evaluated using Aβ1-42-induced Alzheimer's rat model. Lastly, their involvement in Wnt/β-catenin pathway was also demonstrated. The results indicated good CNS penetration for 7m and 7q. The neuroprotective effects of 7m and 7q were evidenced by improved cognitive ability in both scopolamine and Aβ1-42-induced Alzheimer's-like condition in rodents. The in vivo results also confirmed their anti-cholinesterase and anti-oxidant potential. Immunoblot results showed that treatment with 7m and 7q decreased Aβ1-42, p-tau, cleaved caspase-3, and cleaved PARP levels in Aβ1-42-induced Alzheimer's rat brain. Additionally, immunoblot results demonstrated that 7m and 7q activated the Wnt/β-catenin pathway as evidenced by increased p-GSK-3, β-catenin, and neuroD1 levels in Aβ1-42-induced Alzheimer's rat brain. These findings have shown that isoalloxazine derivatives (7m and 7q) could be the potential leads for developing effective drugs for the treatment of AD.

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

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

Is L-methionine a trigger factor for Alzheimer's-like neurodegeneration?: Changes in Aβ oligomers, tau phosphorylation, synaptic proteins, Wnt signaling and behavioral impairment in wild-type mice

BACKGROUND

L-methionine, the principal sulfur-containing amino acid in proteins, plays critical roles in cell physiology as an antioxidant and in the breakdown of fats and heavy metals. Previous studies suggesting the use of L-methionine as a treatment for depression and other diseases indicate that it might also improve memory and propose a role in brain function. However, some evidence indicates that an excess of methionine can be harmful and can increase the risk of developing Type-2 diabetes, heart diseases, certain types of cancer, brain alterations such as schizophrenia, and memory impairment.

RESULTS

Here, we report the effects of an L-methionine-enriched diet in wild-type mice and emphasize changes in brain structure and function. The animals in our study presented 1) higher levels of phosphorylated tau protein, 2) increased levels of amyloid-β (Aβ)-peptides, including the formation of Aβ oligomers, 3) increased levels of inflammatory response,4) increased oxidative stress, 5) decreased level of synaptic proteins, and 6) memory impairment and loss. We also observed dysfunction of the Wnt signaling pathway.

CONCLUSION

Taken together, the results of our study indicate that an L-methionine-enriched diet causes neurotoxic effects in vivo and might contribute to the appearance of Alzheimer's-like neurodegeneration.

Luteinizing hormone as a key player in the cognitive decline of Alzheimer's disease

This article is part of a Special Issue "SBN 2014". Alzheimer's disease is one of the most prevalent and costly neurological diseases in the world. Although decades of research have focused on understanding Alzheimer's disease pathology and progression, there is still a great lack of clinical treatments for those who suffer from it. One of the factors most commonly associated with the onset of Alzheimer's disease is a decrease in levels of gonadal hormones, such as estrogens and androgens. Despite the correlational and experimental data which support the role of these hormones in the etiology of Alzheimer's disease, clinical trials involving their reintroduction through hormone therapy have had varied results and these gonadal hormones often have accompanying health risks. More recently, investigation has turned toward other hormones in the hypothalamic-pituitary-gonadal axis that are disrupted by age-related decreases in gonadal hormones. Specifically, luteinizing hormone, which is increased with age in both men and women (in response to removal of negative feedback), has surfaced as a potentially powerful player in the risk and onset of Alzheimer's disease. Mounting evidence in basic research and epidemiological studies supports the role of elevated luteinizing hormone in exacerbating age-related cognitive decline in both males and females. This review summarizes the recent developments involving luteinizing hormone in increasing the cognitive deficits and molecular pathology characteristic of Alzheimer's disease.

Therapeutic Actions of the Thiazolidinediones in Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial metabolic brain disorder characterized by protein aggregates, synaptic failure, and cognitive impairment. In the AD brain is common to observe the accumulation of senile plaques formed by amyloid-beta (Aβ) peptide and the neurofibrillary tangles composed of modified tau protein, which both lead to cellular damage and progressive neurodegeneration. Currently, there is no effective therapy for AD; however several studies have shown that the treatments with the peroxisome proliferators activated receptor-gamma (PPARγ) agonists known as thiazolidinedione drugs (TZDs), like rosiglitazone and pioglitazone, attenuate neurodegeneration and improve cognition in mouse models and patients with mild-to-moderate AD. Furthermore, studies on animal models have shown that TZDs inhibit neuroinflammation, facilitate amyloid-β plaque clearance, enhance mitochondrial function, improve synaptic plasticity, and, more recently, attenuate tau hyperphosphorylation. How TZDs may improve or reduce these pathologic signs of AD and what the mechanisms and the implicated pathways in which these drugs work are are questions that remain to be answered. However, in this review, we will discuss several cellular targets, in which TZDs can be acting against the neurodegeneration.

Osthole promotes neuronal differentiation and inhibits apoptosis via Wnt/β-catenin signaling in an Alzheimer's disease model

Neurogenesis is the process by which neural stem cells (NSCs) proliferate and differentiate into neurons. This is diminished in several neurodegenerative disorders such as Alzheimer's disease (AD), which is characterized by the deposition of amyloid (A)β peptides and neuronal loss. Stimulating NSCs to replace lost neurons is therefore a promising approach for AD treatment. Our previous study demonstrated that osthole modulates NSC proliferation and differentiation, and may reduce Aβ protein expression in nerve cells. Here we investigated the mechanism underlying the effects of osthole on NSCs. We found that osthole enhances NSC proliferation and neuronal differentiation while suppressing apoptosis, effects that were exerted via activation of Wnt/β-catenin signaling. These results provide evidence that osthole can potentially be used as a therapeutic agent in the treatment of AD and other neurodegenerative disorders.

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.

Combined Liver X Receptor/Peroxisome Proliferator-activated Receptor γ Agonist Treatment Reduces Amyloid β Levels and Improves Behavior in Amyloid Precursor Protein/Presenilin 1 Mice

Alzheimer disease (AD) is characterized by the extracellular accumulation of amyloid β (Aβ), which is accompanied by a robust inflammatory response in the brain. Both of these pathogenic processes are regulated by nuclear receptors, including the liver X receptors (LXRs) and peroxisome-proliferator receptor γ (PPARγ). Agonists of LXRs have been demonstrated previously to reduce Aβ levels and improve cognitive deficits in AD mouse models by inducing the transcription and lipidation of apolipoprotein E (apoE). Agonists targeting PPARγ reduce the microglial expression of proinflammatory genes and have also been shown to modulate apoE expression. Here we investigate whether a combination therapy with both LXR and PPARγ agonists results in increased benefits in an AD mouse model. We found that the LXR agonist GW3965 and the PPARγ agonist pioglitazone were individually able to increase the levels of apoE and related genes, decrease the expression of proinflammatory genes, and facilitate Aβ decreases in the hippocampus. Combined treatment with both agonists provoked a further increase in the expression of apoE and a decrease in the soluble and deposited forms of Aβ. The decrease in plaques was associated with increased colocalization between microglia and plaques. In addition, the PPARγ agonist in the combined treatment paradigm was able to counteract the elevation in plasma triglycerides that is a side effect of LXR agonist treatment. These results suggest that combined LXR/PPARγ agonist treatment merits further investigation for the treatment of AD.

Soluble amyloid-β oligomers as synaptotoxins leading to cognitive impairment in Alzheimer's disease

Alzheimer’s disease (AD) is the most common form of dementia in the elderly, and affects millions of people worldwide. As the number of AD cases continues to increase in both developed and developing countries, finding therapies that effectively halt or reverse disease progression constitutes a major research and public health challenge. Since the identification of the amyloid-β peptide (Aβ) as the major component of the amyloid plaques that are characteristically found in AD brains, a major effort has aimed to determine whether and how Aβ leads to memory loss and cognitive impairment. A large body of evidence accumulated in the past 15 years supports a pivotal role of soluble Aβ oligomers (AβOs) in synapse failure and neuronal dysfunction in AD. Nonetheless, a number of basic questions, including the exact molecular composition of the synaptotoxic oligomers, the identity of the receptor(s) to which they bind, and the signaling pathways that ultimately lead to synapse failure, remain to be definitively answered. Here, we discuss recent advances that have illuminated our understanding of the chemical nature of the toxic species and the deleterious impact they have on synapses, and have culminated in the proposal of an Aβ oligomer hypothesis for Alzheimer’s pathogenesis. We also highlight outstanding questions and challenges in AD research that should be addressed to allow translation of research findings into effective AD therapies.

Role of Wnt Signaling in Central Nervous System Injury

The central nervous system (CNS) is highly sensitive to external mechanical damage, presenting a limited capacity for regeneration explained in part by its inability to restore either damaged neurons or the synaptic network. The CNS may suffer different types of external injuries affecting its function and/or structure, including stroke, spinal cord injury, and traumatic brain injury. These pathologies critically affect the quality of life of a large number of patients worldwide and are often fatal because available therapeutics are ineffective and produce limited results. Common effects of the mentioned pathologies involves the triggering of several cellular and metabolic responses against injury, including infiltration of blood cells, inflammation, glial activation, and neuronal death. Although some of the underlying molecular mechanisms of those responses have been elucidated, the mechanisms driving these processes are poorly understood in the context of CNS injury. In the last few years, it has been suggested that the activation of the Wnt signaling pathway could be important in the regenerative response after CNS injury, activating diverse protective mechanisms including the stimulation of neurogenesis, blood brain structure consolidation and the recovery of cognitive brain functions. Because Wnt signaling is involved in several physiological processes, the putative positive role of its activation after injury could be the basis for novel therapeutic approaches to CNS injury.

Voluntary Running Attenuates Memory Loss, Decreases Neuropathological Changes and Induces Neurogenesis in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by loss of memory and cognitive abilities, and the appearance of amyloid plaques composed of the amyloid-β peptide (Aβ) and neurofibrillary tangles formed of tau protein. It has been suggested that exercise might ameliorate the disease; here, we evaluated the effect of voluntary running on several aspects of AD including amyloid deposition, tau phosphorylation, inflammatory reaction, neurogenesis and spatial memory in the double transgenic APPswe/PS1ΔE9 mouse model of AD. We report that voluntary wheel running for 10 weeks decreased Aβ burden, Thioflavin-S-positive plaques and Aβ oligomers in the hippocampus. In addition, runner APPswe/PS1ΔE9 mice showed fewer phosphorylated tau protein and decreased astrogliosis evidenced by lower staining of GFAP. Further, runner APPswe/PS1ΔE9 mice showed increased number of neurons in the hippocampus and exhibited increased cell proliferation and generation of cells positive for the immature neuronal protein doublecortin, indicating that running increased neurogenesis. Finally, runner APPswe/PS1ΔE9 mice showed improved spatial memory performance in the Morris water maze. Altogether, our findings indicate that in APPswe/PS1ΔE9 mice, voluntary running reduced all the neuropathological hallmarks of AD studied, reduced neuronal loss, increased hippocampal neurogenesis and reduced spatial memory loss. These findings support that voluntary exercise might have therapeutic value on AD.

How the Wnt signaling pathway protects from neurodegeneration: the mitochondrial scenario

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and is characterized by progressive memory loss and cognitive decline. One of the hallmarks of AD is the overproduction of amyloid-beta aggregates that range from the toxic soluble oligomer (Aβo) form to extracellular accumulations in the brain. Growing evidence indicates that mitochondrial dysfunction is a common feature of neurodegenerative diseases and is observed at an early stage in the pathogenesis of AD. Reports indicate that mitochondrial structure and function are affected by Aβo and can trigger neuronal cell death. Mitochondria are highly dynamic organelles, and the balance between their fusion and fission processes is essential for neuronal function. Interestingly, in AD, the process known as “mitochondrial dynamics” is also impaired by Aβo. On the other hand, the activation of the Wnt signaling pathway has an essential role in synaptic maintenance and neuronal functions, and its deregulation has also been implicated in AD. We have demonstrated that canonical Wnt signaling, through the Wnt3a ligand, prevents the permeabilization of mitochondrial membranes through the inhibition of the mitochondrial permeability transition pore (mPTP), induced by Aβo. In addition, we showed that non-canonical Wnt signaling, through the Wnt5a ligand, protects mitochondria from fission-fusion alterations in AD. These results suggest new approaches by which different Wnt signaling pathways protect neurons in AD, and support the idea that mitochondria have become potential therapeutic targets for the treatment of neurodegenerative disorders. Here we discuss the neuroprotective role of the canonical and non-canonical Wnt signaling pathways in AD and their differential modulation of mitochondrial processes, associated with mitochondrial dysfunction and neurodegeneration.

Differential proteomic and behavioral effects of long-term voluntary exercise in wild-type and APP-overexpressing transgenics

Physical exercise may provide protection against the cognitive decline and neuropathology associated with Alzheimer's disease, although the mechanisms are not clear. In the present study, APP/PSEN1 double-transgenic and wild-type mice were allowed unlimited voluntary exercise for 7months. Consistent with previous reports, wheel-running improved cognition in the double-transgenic mice. Interestingly, the average daily distance run was strongly correlated with spatial memory in the water maze in wild-type mice (r(2)=.959), but uncorrelated in transgenics (r(2)=.013). Proteomics analysis showed that sedentary transgenic mice differed significantly from sedentary wild-types with respect to proteins involved in synaptic transmission, cytoskeletal regulation, and neurogenesis. When given an opportunity to exercise, the transgenics' deficiencies in cytoskeletal regulation and neurogenesis largely normalized, but abnormal synaptic proteins did not change. In contrast, exercise enhanced proteins associated with cytoskeletal regulation, oxidative phosphorylation, and synaptic transmission in wild-type mice. Soluble and insoluble Aβ40 and Aβ42 levels were significantly decreased in both cortex and hippocampus of active transgenics, suggesting that this may have played a role in the cognitive improvement in APP/PSEN1 mice. β-secretase was significantly reduced in active APP/PSEN1 mice compared to sedentary controls, suggesting a mechanism for reduced Aβ. Taken together, these data illustrate that exercise improves memory in wild-type and APP-overexpressing mice in fundamentally different ways.

Andrographolide activates the canonical Wnt signalling pathway by a mechanism that implicates the non-ATP competitive inhibition of GSK-3β: autoregulation of GSK-3β in vivo

Andrographolide activates the canonical Wnt pathway and induces the transcription of Wnt target genes through a mechanism independent of Wnt ligand binding to its receptor, by direct substrate-competitive inhibition of GSK-3.

Glycogen synthase kinase-3 as a therapeutic target for cognitive dysfunction in neuropsychiatric disorders

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) is involved in a broad range of cellular processes including cell proliferation, apoptosis and inflammation. It is now also increasingly acknowledged as having a role to play in cognitive-related processes such as neurogenesis, synaptic plasticity and neural cell survival. Cognitive impairment represents a major debilitating feature of many neurodegenerative and psychiatric disorders, including Alzheimer's disease, mood disorders, schizophrenia and fragile X syndrome, as well as being a result of traumatic brain injury or cranial irradiation. Accordingly, GSK-3 has been identified as an important therapeutic target for cognitive impairment, and recent preclinical studies have yielded important evidence demonstrating that GSK-3 inhibitors may be useful therapeutic interventions for restoring cognitive function in some of these brain disorders. The current review summarises the role of GSK-3 as a regulator of cognitive-dependent functions, examines current preclinical and clinical evidence of the potential of GSK-3 inhibitors as therapeutic agents for cognitive impairments in neuropsychiatric disorders, and offers some insight into the current obstacles that are impeding the clinical use of selective GSK-3 inhibitors in the treatment of cognitive impairment.

The protein oxidation repair enzyme methionine sulfoxide reductase a modulates Aβ aggregation and toxicity in vivo

AIMS

To examine the role of the enzyme methionine sulfoxide reductase A-1 (MSRA-1) in amyloid-β peptide (Aβ)-peptide aggregation and toxicity in vivo, using a Caenorhabditis elegans model of the human amyloidogenic disease inclusion body myositis.

RESULTS

MSRA-1 specifically reduces oxidized methionines in proteins. Therefore, a deletion of the msra-1 gene was introduced into transgenic C. elegans worms that express the Aβ-peptide in muscle cells to prevent the reduction of oxidized methionines in proteins. In a constitutive transgenic Aβ strain that lacks MSRA-1, the number of amyloid aggregates decreases while the number of oligomeric Aβ species increases. These results correlate with enhanced synaptic dysfunction and mislocalization of the nicotinic acetylcholine receptor ACR-16 at the neuromuscular junction (NMJ).

INNOVATION

This approach aims at modulating the oxidation of Aβ in vivo indirectly by dismantling the methionine sulfoxide repair system. The evidence presented here shows that the absence of MSRA-1 influences Aβ aggregation and aggravates locomotor behavior and NMJ dysfunction. The results suggest that therapies which boost the activity of the Msr system could have a beneficial effect in managing amyloidogenic pathologies.

CONCLUSION

The absence of MSRA-1 modulates Aβ-peptide aggregation and increments its deleterious effects in vivo.

Natural compounds with Wnt signal modulating activity

This article highlights natural compounds that are reported to modulate the Wnt signalling activity. The plausible mechanisms of action of the natural Wnt modulators are also presented.

Role of adult hippocampal neurogenesis in cognition in physiology and disease: pharmacological targets and biomarkers

Adult hippocampal neurogenesis is a remarkable form of brain structural plasticity by which new functional neurons are generated from adult neural stem cells/precursors. Although the precise role of this process remains elusive, adult hippocampal neurogenesis is important for learning and memory and it is affected in disease conditions associated with cognitive impairment, depression, and anxiety. Immature neurons in the adult brain exhibit an enhanced structural and synaptic plasticity during their maturation representing a unique population of neurons to mediate specific hippocampal function. Compelling preclinical evidence suggests that hippocampal neurogenesis is modulated by a broad range of physiological stimuli which are relevant in cognitive and emotional states. Moreover, multiple pharmacological interventions targeting cognition modulate adult hippocampal neurogenesis. In addition, recent genetic approaches have shown that promoting neurogenesis can positively modulate cognition associated with both physiology and disease. Thus the discovery of signaling pathways that enhance adult neurogenesis may lead to therapeutic strategies for improving memory loss due to aging or disease. This chapter endeavors to review the literature in the field, with particular focus on (1) the role of hippocampal neurogenesis in cognition in physiology and disease; (2) extrinsic and intrinsic signals that modulate hippocampal neurogenesis with a focus on pharmacological targets; and (3) efforts toward novel strategies pharmacologically targeting neurogenesis and identification of biomarkers of human neurogenesis.

Andrographolide reduces cognitive impairment in young and mature AβPPswe/PS-1 mice

Alzheimer’s disease (AD) is a neurodegenerative disorder in which the amyloid-β (Aβ) oligomers are a key factor in synaptic impairment and in spatial memory decline associated with neuronal dysfunction. This impairment includes synaptic failure associated with the loss of synaptic proteins that contribute to AD progression. Interestingly, the use of natural compounds is an emergent conceptual strategy in the search for drugs with therapeutic potentials for treating neurodegenerative disorders. In the present study, we report that andrographolide (ANDRO), which is a labdane diterpene extracted from Andrographis paniculata, increases slope of field excitatory postsynaptic potentials (fEPSP) in the CA1 region of hippocampal slices and inhibits long-term depression (LTD), protecting the long-term potentiation (LTP) against the damage induced by Aβ oligomers in vitro, most likely by inhibiting glycogen synthase kinase-3β (GSK-3β). Additionally, ANDRO prevents changes in neuropathology in two different age groups (7- and 12-month-old mice) of an AβPPswe/PS-1 Alzheimer’s model. ANDRO reduces the Aβ levels, changing the ontogeny of amyloid plaques in hippocampi and cortices in 7-month-old mice, and reduces tau phosphorylation around the Aβ oligomeric species in both age groups. Additionally, we observed that ANDRO recovers spatial memory functions that correlate with protecting synaptic plasticity and synaptic proteins in two different age groups. Our results suggest that ANDRO could be used in a potential preventive therapy during AD progression.

Nuclear receptors in neurodegenerative diseases

Nuclear receptors have generated substantial interest in the past decade as potential therapeutic targets for the treatment of neurodegenerative disorders. Despite years of effort, effective treatments for progressive neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease and ALS remain elusive, making non-classical drug targets such as nuclear receptors an attractive alternative. A substantial literature in mouse models of disease and several clinical trials have investigated the role of nuclear receptors in various neurodegenerative disorders, most prominently AD. These studies have met with mixed results, yet the majority of studies in mouse models report positive outcomes. The mechanisms by which nuclear receptor agonists affect disease pathology remain unclear. Deciphering the complex signaling underlying nuclear receptor action in neurodegenerative diseases is essential for understanding this variability in preclinical studies, and for the successful translation of nuclear receptor agonists into clinical therapies.

Lack of evidence of the interaction of the Aβ peptide with the Wnt signaling cascade in Drosophila models of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the leading form of dementia worldwide. The Aβ-peptide is believed to be the major pathogenic compound of the disease. Since several years it is hypothesized that Aβ impacts the Wnt signaling cascade and therefore activation of this signaling pathway is proposed to rescue the neurotoxic effect of Aβ.

Findings

Expression of the human Aβ42 in the Drosophila nervous system leads to a drastically shortened life span. We found that the action of Aβ42 specifically in the glutamatergic motoneurons is responsible for the reduced survival. However, we find that the morphology of the glutamatergic larval neuromuscular junctions, which are widely used as the model for mammalian central nervous system synapses, is not affected by Aβ42 expression. We furthermore demonstrate that genetic activation of the Wnt signal transduction pathway in the nervous system is not able to rescue the shortened life span or a rough eye phenotype in Drosophila.

Conclusions

Our data confirm that the life span is a useful readout of Aβ42 induced neurotoxicity in Drosophila; the neuromuscular junction seems however not to be an appropriate model to study AD in flies. Additionally, our results challenge the hypothesis that Wnt signaling might be implicated in Aβ42 toxicity and might serve as a drug target against AD.

Treatment of vascular risk factors in patients with a diagnosis of Alzheimer's disease: a systematic review

BACKGROUND

Increasing evidence suggests vascular risk factors (VRF) play a role in the pathogenesis of Alzheimer's disease (AD). Epidemiological studies have found associations between VRF and risk of AD. Treating VRF in patients with AD offers a potential treatment option but ineffective treatments should be avoided in this group who are frequently on multiple medications and in whom compliance may be challenging.

METHODS

Studies containing information on the treatment of VRF in patients with a diagnosis of AD were identified using a defined search strategy. Randomised controlled trials and observational studies were included.

RESULTS

The pre-specified search strategy retrieved 11,992 abstract articles, and 25 papers including those identified on review of reference lists and reviews met the inclusion criteria. Of these, 11 were randomised controlled trials (RCTs) and 14 observational studies. Observational studies suggested that a VRF package and treatment of hypertension and statin therapy may be associated with improved outcome but these studies suffered from potential bias. The few RCTs performed were mostly small with short duration follow-up, and do not provide clear evidence either way.

CONCLUSIONS

Observational data raises the possibility that treating VRF could alter the rate of decline in AD. However RCT data are not yet available to support this hypothesis and to alter clinical practice. RCTs in larger numbers of individuals with longer follow-up, ideally in the early stages of AD, are required to address this potentially important treatment question.

Common biological mechanisms between bipolar disorder and type 2 diabetes: Focus on inflammation

INTRODUCTION

Bipolar disorder (BD) patients present a 3-5 fold greater risk of developing type 2 diabetes (T2D) compared to general population. The underlying mechanisms for the increased prevalence of T2D in BD population are poorly understood.

OBJECTIVES

The purpose of this review is to critically review evidence suggesting that inflammation may have an important role in the development of both BD and T2D.

RESULTS

The literature covered in this review suggests that inflammatory dysregulation take place among many BD patients. Such dysregulated and low grade chronic inflammatory process may also increase the prevalence of T2D in BD population. Current evidence supports the hypothesis of dysregulated inflammatory processes as a critical upstream event in BD as well as in T2D.

CONCLUSIONS

Inflammation may be a factor for the development of T2D in BD population. The identification of inflammatory markers common to these two medical conditions will enable researchers and clinicians to better understand the etiology of BD and develop treatments that simultaneously target all aspects of this multi-system condition.

Wnt signalling in neuronal differentiation and development

Wnts are secreted glycoproteins that play multiple roles in early development, including the differentiation of precursor cells. During this period, gradients of Wnts and other morphogens are formed and regulate the differentiation and migration of neural progenitor cells. Afterwards, Wnt signalling cascades participate in the formation of neuronal circuits, playing roles in dendrite and axon development, dendritic spine formation and synaptogenesis. Finally, in the adult brain, Wnts control hippocampal plasticity, regulating synaptic transmission and neurogenesis. In this review, we summarize the reported roles of Wnt signalling cascades in these processes with a particular emphasis on the role of Wnts in neuronal differentiation and development.

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.