Association between glycogen synthase kinase-3beta genetic polymorphism and late-onset Alzheimer's disease

Cyanidin Ameliorates Bisphenol A-Induced Alzheimer's Disease Pathology by Restoring Wnt/β-Catenin Signaling Cascade: an In Vitro Study

Alzheimer's disease (AD) is a progressive neurodegenerative disorder causing memory loss and cognitive decline, linked to amyloid-beta (Aβ) plaques and hyperphosphorylated tau protein accumulation in the brain. Environmental pollutant bisphenol A (BPA) has been implicated in AD pathology due to its neurotoxic effects. This study aims to evaluate cyanidin from flower bracts of Musa acuminata Colla (red variety; AAA group) for its neuroprotective properties against BPA-induced AD pathology. The extraction of cyanidin was optimized using 70% ethanol in acidified water, showing promising anti-acetylcholinesterase activity. Cyanidin was effectively purified from the resultant extract and characterized using spectroscopic techniques. Two gradient doses of cyanidin (90 and 10 µg/ml) were determined based on cell viability assay. The role of cyanidin in promoting nerve growth and differentiation was assessed in PC12 cells for up to 72 h. A discernible and statistically significant difference was assessed in neurite extension at both doses at 72 h, followed by pre-treatment with cyanidin. BPA stimulation significantly increased the p-tau expression compared to the control (p < 0.0001). Pre-treatment with cyanidin reduced the tau expression; however, a significant difference was observed compared to control cells (p = 0.0003). Cyanidin significantly enhanced the mRNA expression of Wnt3a (p < 0.0001), β-catenin (p = 0.0004), and NeuroD1 (p = 0.0289), and decreased the expression of WIF1(p = 0.0040) and DKK1 (p < 0.0001), which are Wnt antagonist when compared to cells stimulated with BPA. Conclusively, our finding suggests that cyanidin could agonize nerve growth factor and promote neuronal differentiation, reduce tau-hyperphosphorylation by restoring the Wnt/β-catenin signaling cascade, and thereby render its neuroprotective potential against BPA-induced AD pathology.

Neurogenomics of Alzheimer's Disease (AD): An Asian Population Review

Alzheimer's disease (AD) is on the rise worldwide. Generally, AD is considered neurodegenerative when the production and clearance of amyloid-β (Aβ) are imbalanced. Recent research on genome-wide association studies (GWAS) has been explosive; GWAS indicates a relationship between single nucleotide polymorphism (SNP) and AD. GWAS also reveals ethnic differences between Caucasians and Asians. This indicates that pathogenesis between ethnic groups is distinct. According to current scientific knowledge, AD is a disease with a complex pathogenesis that includes impaired neuronal cholesterol regulation, immunity regulation, neurotransmitters regulation, Aβ clearance, Aβ production, and vascular regulation. Here, we demonstrate the pathogenesis of AD in an Asian population and the SNP risk of AD for future AD screening before onset. According to our knowledge, this is the first review of Alzheimer's disease to demonstrate the pathogenesis of AD based on SNP in an Asian population.

SYK coordinates neuroprotective microglial responses in neurodegenerative disease

Recent studies have begun to reveal critical roles for the brain's professional phagocytes, microglia, and their receptors in the control of neurotoxic amyloid beta (Aβ) and myelin debris accumulation in neurodegenerative disease. However, the critical intracellular molecules that orchestrate neuroprotective functions of microglia remain poorly understood. In our studies, we find that targeted deletion of SYK in microglia leads to exacerbated Aβ deposition, aggravated neuropathology, and cognitive defects in the 5xFAD mouse model of Alzheimer's disease (AD). Disruption of SYK signaling in this AD model was further shown to impede the development of disease-associated microglia (DAM), alter AKT/GSK3β-signaling, and restrict Aβ phagocytosis by microglia. Conversely, receptor-mediated activation of SYK limits Aβ load. We also found that SYK critically regulates microglial phagocytosis and DAM acquisition in demyelinating disease. Collectively, these results broaden our understanding of the key innate immune signaling molecules that instruct beneficial microglial functions in response to neurotoxic material.

Hypermethylation of Mest promoter causes aberrant Wnt signaling in patients with Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and behavioral changes. Extracellular deposition of amyloid plaques (Aβ) and intracellular deposition of neurofibrillary tangles in neurons are the major pathogenicities of AD. However, drugs targeting these therapeutic targets are not effective. Therefore, novel targets for the treatment of AD urgently need to be identified. Expression of the mesoderm-specific transcript (Mest) is regulated by genomic imprinting, where only the paternal allele is active for transcription. We identified hypermethylation on the Mest promoter, which led to a reduction in Mest mRNA levels and activation of Wnt signaling in brain tissues of AD patients. Mest knockout (KO) using the CRIPSR/Cas9 system in mouse embryonic stem cells and P19 embryonic carcinoma cells leads to neuronal differentiation arrest. Depletion of Mest in primary hippocampal neurons via lentivirus expressing shMest or inducible KO system causes neurodegeneration. Notably, depletion of Mest in primary cortical neurons of rats leads to tau phosphorylation at the S199 and T231 sites. Overall, our data suggest that hypermethylation of the Mest promoter may cause or facilitate the progression of AD.

WNT Signaling Is a Key Player in Alzheimer's Disease

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

Dysregulated Wnt Signalling in the Alzheimer's Brain

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

Dickkopf-related protein-1 inhibition attenuates amyloid-beta pathology associated to Alzheimer's disease

Alzheimer's disease (AD) constitutes the leading cause of dementia worldwide. It is associated to amyloid-β (Aβ) aggregation and tau hyper-phosphorylation, accompanied by a progressive cognitive decline. Evidence suggests that the canonical Wnt pathway is deregulated in AD. Pathway activity is mediated by β-catenin stabilization in the cytosol, and subsequent translocation to the nucleus to regulate the expression of several genes implicated in brain homeostasis and functioning. It was recently proposed that Dickkopf-related protein-1 (DKK1), an endogenous antagonist of the pathway, might be implicated in AD pathogenesis. Here, we hypothesized that canonical Wnt pathway deactivation associated to DKK1 induction contributes to late-onset AD pathogenesis, and thus DKK1 neutralization could attenuate AD pathology. For this purpose, human post-mortem AD brain samples were used to assess pathway activity, and aged APPswe/PS1 mice were used to investigate DKK1 in late-onset AD-like pathology and therapy. Our findings indicate that β-catenin levels progressively decrease in the brain of AD patients, correlating with the duration of symptoms. Next, we found that Aβ pathology in APPswe/PS1 mediates DKK1 induction in the brain. Pharmacological neutralization of DKK1's biological activity in APPswe/PS1 mice restores pathway activity by stabilizing β-catenin, attenuates Aβ pathology, and ameliorates the memory of mice. Attenuation of AD-like pathology upon DKK1 inhibition is accompanied by a reduced protein expression of beta-site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1). Moreover, DKK1 inhibition enhances vascular density, promotes blood-brain barrier (BBB) integrity by increasing claudin 5, glucose transporter-1 (GLUT1), and ATP-binding cassette sub-family B member-1 (ABCB1) protein expression, as well as ameliorates synaptic plasticity by increasing brain-derived neurotrophic factor (BDNF), and postsynaptic density protein-95 (PSD-95) protein expression. DKK1 conditional induction reduces claudin 5, abcb1, and psd-95 mRNA expression, validating its inhibition effects. Our results indicate that neutralization of DKK1's biological activity attenuates AD-like pathology by restoring canonical Wnt pathway activity.

Could Alzheimer's Disease Originate in the Periphery and If So How So?

The classical amyloid cascade model for Alzheimer's disease (AD) has been challenged by several findings. Here, an alternative molecular neurobiological model is proposed. It is shown that the presence of the APOE ε4 allele, altered miRNA expression and epigenetic dysregulation in the promoter region and exon 1 of TREM2, as well as ANK1 hypermethylation and altered levels of histone post-translational methylation leading to increased transcription of TNFA, could variously explain increased levels of peripheral and central inflammation found in AD. In particular, as a result of increased activity of triggering receptor expressed on myeloid cells 2 (TREM-2), the presence of the apolipoprotein E4 (ApoE4) isoform, and changes in ANK1 expression, with subsequent changes in miR-486 leading to altered levels of protein kinase B (Akt), mechanistic (previously mammalian) target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3), all of which play major roles in microglial activation, proliferation and survival, there is activation of microglia, leading to the subsequent (further) production of cytokines, chemokines, nitric oxide, prostaglandins, reactive oxygen species, inducible nitric oxide synthase and cyclooxygenase-2, and other mediators of inflammation and neurotoxicity. These changes are associated with the development of amyloid and tau pathology, mitochondrial dysfunction (including impaired activity of the electron transport chain, depleted basal mitochondrial potential and oxidative damage to key tricarboxylic acid enzymes), synaptic dysfunction, altered glycogen synthase kinase-3 (GSK-3) activity, mTOR activation, impairment of autophagy, compromised ubiquitin-proteasome system, iron dyshomeostasis, changes in APP translation, amyloid plaque formation, tau hyperphosphorylation and neurofibrillary tangle formation.

Knowledge-Based Neuroendocrine Immunomodulation (NIM) Molecular Network Construction and Its Application

Growing evidence shows that the neuroendocrine immunomodulation (NIM) network plays an important role in maintaining and modulating body function and the homeostasis of the internal environment. The disequilibrium of NIM in the body is closely associated with many diseases. In the present study, we first collected a core dataset of NIM signaling molecules based on our knowledge and obtained 611 NIM signaling molecules. Then, we built a NIM molecular network based on the MetaCore database and analyzed the signaling transduction characteristics of the core network. We found that the endocrine system played a pivotal role in the bridge between the nervous and immune systems and the signaling transduction between the three systems was not homogeneous. Finally, employing the forest algorithm, we identified the molecular hub playing an important role in the pathogenesis of rheumatoid arthritis (RA) and Alzheimer’s disease (AD), based on the NIM molecular network constructed by us. The results showed that GSK3B, SMARCA4, PSMD7, HNF4A, PGR, RXRA, and ESRRA might be the key molecules for RA, while RARA, STAT3, STAT1, and PSMD14 might be the key molecules for AD. The molecular hub may be a potentially druggable target for these two complex diseases based on the literature. This study suggests that the NIM molecular network in this paper combined with the forest algorithm might provide a useful tool for predicting drug targets and understanding the pathogenesis of diseases. Therefore, the NIM molecular network and the corresponding online tool will not only enhance research on complex diseases and system biology, but also promote the communication of valuable clinical experience between modern medicine and Traditional Chinese Medicine (TCM).

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

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

GSK-3β, a double-edged sword in Nrf2 regulation: Implications for neurological dysfunction and disease

In the past decade, it has become evident that glycogen synthase kinase 3β (GSK-3β) modulates the nuclear factor erythroid 2-related factor 2 (Nrf2) oxidative stress response. GSK-3β functions as an inhibitor, both directly in the activation and indirectly in the post-induction of Nrf2. The incidence of oxidative stress in neurological dysfunction and disease has made this signaling pathway an attractive therapeutic target. There is minimal evidence, however, to support a distinctive function for GSK-3β mediated Nrf2 inhibition in nervous system decline, apart from the typical oxidative stress response. In both Alzheimer's disease and brain ischemia, this pathway has been explored for potential benefits on disease etiology and advancement. Presently, it is unclear whether GSK-3β mediated Nrf2 inhibition markedly influences these disease states. Furthermore, the potential that each has unique function in neurodegenerative decline is unsubstantiated.

Interactions between four gene polymorphisms and their association with patients with Parkinson's disease in a Chinese Han population

The four previously reported Parkinson's disease (PD)-related single-nucleotide polymorphisms (SNPs) - rs1775143, rs823114, rs2071746 and rs62063857 - have rarely been studied in Chinese Han populations. To examine the association between these SNPs and PD, we conducted a case-control study of 158 patients with PD and 210 controls. All participants were Chinese Han from Northern China. With covariate adjustment for clinical characteristics, logistic regression analysis revealed no differences in genotype or allele frequencies for the four SNPs. Stratified by age of disease onset, sex, smoking status, duration of disease, baseline UPDRS, Hoehn-Yahr Stage, PD subtypes, scores of Hamilton anxiety scale, Hamilton depression scale and activity of daily living, all of the p values did not remain significant after Bonferroni correction. However, the haplotype rs1775143T-rs823114G-rs2071746T-rs62063857A was associated with increased risk of developing PD (p = 0.003, OR = 456.88, 95% CI: 27.40-7619.75) in our case-control sample set. The haplotype rs1775143T-rs823114G-rs2071746T was also associated with increased risk of developing PD (p = 0.003, OR = 338.43, 95% CI: 20.68-5538.27). Although the haplotype rs1775143T-rs823114G-rs62063857A was associated with increased risk of PD (p = 0.03), the 95% CI was 0.993-22.469. Our data demonstrate that although specific SNPs were not related with PD patients, certain haplotypes were associated with increased risk for PD in the Chinese Han population. These results provide further evidence that the etiology of PD is multifactorial, although the underling mechanism needs further study.

Saitohin Q7R polymorphism is associated with late-onset Alzheimer's disease susceptibility among caucasian populations: a meta-analysis

Saitohin (STH) Q7R polymorphism has been reported to influence the individual's susceptibility to Alzheimer's disease (AD); however, conclusions remain controversial. Therefore, we performed this meta-analysis to explore the association between STH Q7R polymorphism and AD risk. Systematic literature searches were performed in the PubMed, Embase, Cochrane Library and Web of Science for studies published before 31 August 2016. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the strength of the association using a fixed- or random-effects model. Subgroup analyses, Galbraith plot and sensitivity analyses were also performed. All statistical analyses were performed with STATA Version 12.0. A total of 19 case-control studies from 17 publications with 4387 cases and 3972 controls were included in our meta-analysis. The results showed that the Q7R polymorphism was significantly associated with an increased risk of AD in a recessive model (RR versus QQ+QR, OR = 1.27, 95% CI = 1.01-1.60, P = 0.040). After excluding the four studies not carried out in caucasians, the overall association was unchanged in all comparison models. Further subgroup analyses stratified by the time of AD onset, and the quality of included studies provided statistical evidence of significant increased risk of AD in RR versus QQ+QR model only in late-onset subjects (OR = 1.56, 95% CI = 1.07-2.26, P = 0.021) and in studies with high quality (OR = 1.37, 95% CI = 1.01-1.86, P = 0.043). This meta-analysis suggests that the RR genotype in saitohin Q7R polymorphism may be a human-specific risk factor for AD, especially among late-onset AD subjects and caucasian populations.

Common Polymorphisms in the GSK3β Gene May Contribute to the Pathogenesis of Alzheimer Disease: A Meta-Analysis

OBJECTIVE

Although it is well known that GSK3β participates in the proliferation and survival of various tumor cells, its role in diseases of the central nervous system has been sparsely documented. In the past few years, studies regarding the relationship between GSK3β rs334558 T>C and rs6438552 C>T polymorphisms and Alzheimer disease (AD) risk have yielded contradictory results. As such, this meta-analysis seeks to satisfy the need to further investigate this relationship.

METHODS

In this research, published studies regarding the association of GSK3β rs6438552 and rs334558 mutation with AD risk was systematically assessed. Studies were retrieved from MEDLINE, Science Citation Index, the Cochrane Library, PubMed, Embase, CINAHL, Current Contents Index, Chinese Biomedical, Chinese Journal Full-Text, and Weipu Journal. Pooled odds ratios and 95% confidence intervals were calculated for allele contrast and homozygous, heterozygous, dominant, and recessive genetic model comparisons.

RESULTS

It was found that GSK3β rs334558 T>C and rs6438552 C>T polymorphisms were correlated with susceptibility to AD under 4 genetic models (all P<.05). In country-stratified subgroups, the results showed increased risk of developing AD in rs334558 T>C polymorphism among Chinese and Spain populations in majority groups. GSK3β rs6438552 C>T polymorphism was correlated with increased the risk of developing AD only in Australian populations.

CONCLUSION

Our findings suggest that there exists a significant association between GSK3β rs334558 T>C polymorphism and increased susceptibility of AD. Moreover, future updated studies with stratified case-control population are warranted for validation studies.

The association between single nucleotide polymorphisms of GSK 3β gene and sporadic Alzheimer's disease in a cohort of southern Chinese Han population

Recent studies suggest that genetic factors contribute to the pathogenesis of sporadic Alzheimer's disease (sAD). Glycogen synthase kinase-3 beta (GSK 3β) is an important molecule which regulates tau phosphorylation and neurofibrillary tangles formation. GSK 3β gene may be a potential candidate gene for the risk of sAD. To investigate the association of the polymorphisms in GSK 3β gene with sAD, we conducted a case-control study in a southern Chinese Han cohort including 302 sAD patients and 315 control participants. Four single nucleotide polymorphisms (SNPs) (rs3732361, rs56728675, rs60393216, and rs334558) within the promoter region of GSK 3β gene were selected and genotyped with a polymerase chain reaction-ligase detection (PCR-LDR) method. Logistic regression was used to analyze the association between target SNPs and the risk of sAD. After adjusting for age, sex, and APOE ε4 status, no association was revealed between these SNPs and sAD (P > 0.05). The SNPs in the selected regions of GSK 3β gene are unlikely to confer the susceptibility of sAD in southern Chinese Han population. Further studies with a larger sample size and different ethnic populations are needed to reveal the role of SNPs of GSK 3β gene in the pathogenesis of sAD.

The peripheral messenger RNA expression of glycogen synthase kinase-3β genes in Alzheimer's disease patients: a preliminary study

OBJECTIVE

To explore the peripheral leucocytic messenger RNA (mRNA) expression of glycogen synthase kinase-3β (GSK-3β) gene in Alzheimer's disease (AD) patients.

METHODS

Using TaqMan relative quantitative real-time polymerase chain reaction, we analyzed leucocytic gene expression of GSK-3β in 48 AD patients and 49 healthy controls. Clinical data of AD patients were also collected.

RESULTS

The mRNA expression level of the GSK-3β gene was significantly higher in the AD group (3.13±0.62) than in the normal group (2.77±0.77). Correlational analyses showed that the mRNA expression level of GSK-3β gene in AD patients was associated with the age of onset (P=0.047), age (P=0.055), and Behavioral Pathology in Alzheimer's Disease Rating Scale total score (P=0.062) and subscores: aggressiveness score (P=0.073) and anxieties and phobias score (P=0.067). Through multivariate regression model, older age, higher anxieties and phobias score and aggressiveness score were associated with higher mRNA expression level of GSK-3β gene.

CONCLUSION

In AD patients, the mRNA expression level of the GSK-3β gene is increased and may be related to age and behavioural pathology in AD.

Evidence for irreversible inhibition of glycogen synthase kinase-3β by tideglusib

Tideglusib is a GSK-3 inhibitor currently in phase II clinical trials for the treatment of Alzheimer disease and progressive supranuclear palsy. Sustained oral administration of the compound to a variety of animal models decreases Tau hyperphosphorylation, lowers brain amyloid plaque load, improves learning and memory, and prevents neuronal loss. We report here that tideglusib inhibits GSK-3β irreversibly, as demonstrated by the lack of recovery in enzyme function after the unbound drug has been removed from the reaction medium and the fact that its dissociation rate constant is non-significantly different from zero. Such irreversibility may explain the non-competitive inhibition pattern with respect to ATP shown by tideglusib and perhaps other structurally related compounds. The replacement of Cys-199 by an Ala residue in the enzyme seems to increase the dissociation rate, although the drug retains its inhibitory activity with decreased potency and long residence time. In addition, tideglusib failed to inhibit a series of kinases that contain a Cys homologous to Cys-199 in their active site, suggesting that its inhibition of GSK-3β obeys to a specific mechanism and is not a consequence of nonspecific reactivity. Results obtained with [(35)S]tideglusib do not support unequivocally the existence of a covalent bond between the drug and GSK-3β. The irreversibility of the inhibition and the very low protein turnover rate observed for the enzyme are particularly relevant from a pharmacological perspective and could have significant implications on its therapeutic potential.

Glycogen synthase kinase-3β: a mediator of inflammation in Alzheimer's disease?

Proliferation and activation of microglial cells is a neuropathological characteristic of brain injury and neurodegeneration, including Alzheimer's disease. Microglia act as the first and main form of immune defense in the nervous system. While the primary function of microglia is to survey and maintain the cellular environment optimal for neurons in the brain parenchyma by actively scavenging the brain for damaged brain cells and foreign proteins or particles, sustained activation of microglia may result in high production of proinflammatory mediators that disturb normal brain functions and even cause neuronal injury. Glycogen synthase kinase-3β has been recently identified as a major regulator of immune system and mediates inflammatory responses in microglia. Glycogen synthase kinase-3β has been extensively investigated in connection to tau and amyloid β toxicity, whereas reports on the role of this enzyme in neuroinflammation in Alzheimer's disease are negligible. Here we review and discuss the role of glycogen synthase-3β in immune cells in the context of Alzheimer's disease pathology.

GSK3 Function in the Brain during Development, Neuronal Plasticity, and Neurodegeneration

GSK3 has diverse functions, including an important role in brain pathology. In this paper, we address the primary functions of GSK3 in development and neuroplasticity, which appear to be interrelated and to mediate age-associated neurological diseases. Specifically, GSK3 plays a pivotal role in controlling neuronal progenitor proliferation and establishment of neuronal polarity during development, and the upstream and downstream signals modulating neuronal GSK3 function affect cytoskeletal reorganization and neuroplasticity throughout the lifespan. Modulation of GSK3 in brain areas subserving cognitive function has become a major focus for treating neuropsychiatric and neurodegenerative diseases. As a crucial node that mediates a variety of neuronal processes, GSK3 is proposed to be a therapeutic target for restoration of synaptic functioning and cognition, particularly in Alzheimer's disease.

Role of epigenetics in Alzheimer’s and Parkinson’s disease

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are two common neurodegenerative diseases that result in the progressive damage or death of neurons. Environmental agents have the potential to damage the developing and mature nervous system, resulting in neurodegenerative diseases. Heritable changes in gene expression that do not involve coding sequence modifications are referred to as ‘epigenetic’. These modifications include DNA methylation and downstream modification of histones. Environmental factors, including heavy metals and dietary folate intake, perturb neurodegenerative genes by epigenetic means, leading to altered gene expression and late-onset neurodegenerative diseases. Research into the genetic control of DNA methylation indicates an allelic skewing in a significant proportion of genes. This phenomenon may determine how an individual’s genetic makeup can alter the effect an environmental factor has on their risk of developing neurodegeneration. Finally, preliminary evidence using cell culture and transgenic animal models suggests that whole classes of pan-epigenetic modifiers will have significant protective effects against common neurodegenerative diseases.

Peripheral expression of key regulatory kinases in Alzheimer's disease and Parkinson's disease

Alteration of key regulatory kinases may cause aberrant protein phosphorylation and aggregation in Alzheimer's disease (AD) and Parkinson's disease (PD). In this study, we investigated expression and phosphorylation status of glycogen synthase kinase 3 (GSK-3), protein kinase B (Akt) and tau protein in peripheral blood lymphocytes of 20 AD, 25 PD patients and 20 healthy controls. GSK-3 was increased in AD and PD patients. In these latter, GSK-3 levels were positively correlated with daily L-Dopa intake. Phosphorylated Akt expression was augmented in both groups; total Akt levels were increased only in AD patients and were positively correlated with disease duration and severity. Total and phosphorylated tau were increased only in AD, with phospho-tau levels being positively correlated with levels of total tau, Akt, and disease duration. No correlations between protein levels and clinical variables were found in PD patients. Investigation of peripheral changes in the expression of specific kinases may, therefore, lead to the development of innovative biomarkers of neurodegeneration, particularly for AD.

Genetic association of BDNF val66met and GSK-3beta-50T/C polymorphisms with tardive dyskinesia

AIMS

Neurodegenerative processes may be involved in the pathogenesis of tardive dyskinesia (TD), and a growing body of evidence suggests that brain-derived neurotrophic factor (BDNF) plays a role in both the antipsychotic effects and the pathogenesis of TD. BDNF and glycogen synthase kinase (GSK)-3beta are important in neuronal survival, and thus abnormal regulation of BDNF and GSK-3beta may contribute to TD pathophysiology. This study investigated the relationship between two polymorphisms, val66met in the BDNF coding region and -50T/C in the GSK-3beta promoter, and susceptibility to TD among a matched sample of patients having schizophrenia with TD (n = 83), patients with schizophrenia without TD (n = 78), and normal control subjects (n = 93).

METHODS

All subjects were Korean. The BDNF val66met and GSK-3beta-50T/C genotypes were determined by polymerase chain reaction and restriction fragment length polymorphism analyses.

RESULTS

Polymerase chain reaction analysis revealed no significant difference in the occurrence of the polymorphisms among the TD, non-TD, and control subjects, but a significant interaction was observed among the groups possessing BDNF val allele in compound genotypes (P = 0.001). We found that the schizophrenic subjects with the C/C GSK-3beta genotype, who carry the val allele of the BDNF gene, are expected to have a decreased risk of developing neuroleptic-induced tardive dyskinesia (P < 0.001).

CONCLUSIONS

Our results demonstrate that the GSK-3beta C/C genotype with the BDNF val allele is associated with patients having schizophrenia without TD. This study also suggests that the BDNF and GSK-3beta gene polymorphisms work in combination, but not individually, in predisposing patients with schizophrenia to TD.

Epistasis between tau phosphorylation regulating genes (CDK5R1 and GSK-3beta) and Alzheimer's disease risk

OBJECTIVE

Glycogen synthase kinase-3beta (GSK-3beta) and cyclin-dependent kinase 5 (CDK5) have been implicated as two major protein kinases involved in the abnormal hyperphosphorylation of tau in Alzheimer's disease (AD) brain, and the development of neurofibrillary tangles. CDK5 regulatory subunit 1 (CDK5R1) encodes for p35, a protein required for activation of CDK5. As both CDK5R1 and GSK-3beta genes are related to phosphorylation of tau, we examined the combined contribution of these genes to the susceptibility for AD.

METHODS

In a case-control study in 283 AD patients and 263 healthy controls, we examined the combined effects between CDK5R1 (3'-UTR, rs735555) and GSK-3beta (-50, rs334558) polymorphisms on susceptibility to AD.

RESULTS

Subjects carrying both the CDK5R1 (3'-UTR, rs735555) AA genotype and the GSK-3beta (-50, rs334558) CC genotype had a 12.5-fold decrease in AD risk (adjusted by age, sex and APOE status OR = 0.08, 95% CI = 0.01-0.76, P = 0.03), suggesting synergistic effects (epistasis) between both genes.

CONCLUSION

These data support a role for tau phosphorylation regulating genes in risk for AD.

GSK3β polymorphisms, MAPT H1 haplotype and Parkinson's disease in a Greek cohort

To determine whether polymorphisms in the microtubule-associated protein tau (MAPT) and/or glycogen synthase kinase-3β (GSK3β) genes underpin susceptibility to Parkinson's disease (PD), we conducted a case-control association study in a Greek cohort of 196 PD cases and 163 healthy controls. In our study, the MAPT H1 haplotype was found to be significantly associated with PD, no association was detected between the intronic rs6438552 (-157 T/C) GSK3β polymorphism and PD, whereas the C/C genotype of the promoter rs334558 (-50 T/C) GSK3β polymorphism was found to exert a protective role. The C/C genotype of the rs334558 GSK3β polymorphism was also found to have an additional protective role in our MAPT H1/H1 PD subgroup. Haplotype analysis revealed that, the T-T haplotype of both GSK3β polymorphisms was over-represented in PD patients compared to controls, and this association was independent of MAPT H1 haplotype.

Wnt signaling in Alzheimer's disease: up or down, that is the question

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, neuropathologically characterized by amyloid-beta (Abeta) plaques and hyperphosphorylated tau accumulation. AD occurs sporadically (SAD), or is caused by hereditary missense mutations in the amyloid precursor protein (APP) or presenilin-1 and -2 (PSEN1 and PSEN2) genes, leading to early-onset familial AD (FAD). Accumulating evidence points towards a role for altered Wnt/beta-catenin-dependent signaling in the etiology of both forms of AD. Presenilins are involved in modulating beta-catenin stability; therefore FAD-linked PSEN-mediated effects can deregulate the Wnt pathway. Genetic variations in the low-density lipoprotein receptor-related protein 6 and apolipoprotein E in AD have been associated with reduced Wnt signaling. In addition, tau phosphorylation is mediated by glycogen synthase kinase-3 (GSK-3), a key antagonist of the Wnt pathway. In this review, we discuss Wnt/beta-catenin signaling in both SAD and FAD, and recapitulate which of its aberrant functions may be critical for (F)AD pathogenesis. We discuss the intriguing possibility that Abeta toxicity may downregulate the Wnt/beta-catenin pathway, thereby upregulating GSK-3 and consequent tau hyperphosphorylation, linking Abeta and tangle pathology. The currently available evidence implies that disruption of tightly regulated Wnt signaling may constitute a key pathological event in AD. In this context, drug targets aimed at rescuing Wnt signaling may prove to be a constructive therapeutic strategy for AD.

Linking Abeta and tau in late-onset Alzheimer's disease: a dual pathway hypothesis

Alzheimer's disease is characterized by abnormal elevation of Abeta peptide and abnormal hyperphosphorylation of the tau protein. The "amyloid hypothesis," which is based on molecular defects observed in autosomal-dominant early-onset Alzheimer's disease (EOAD), suggests a serial model of causality, whereby elevation of Abeta drives other disease features including tau hyperphosphorylation. Here, we review recent evidence from drug trials, genetic studies, and experimental work in animal models that suggests that an alternative model might exist in late-onset AD (LOAD), the complex and more common form of the disease. Specifically, we hypothesize a "dual pathway" model of causality, whereby Abeta and tau can be linked by separate mechanisms driven by a common upstream driver. This model may account for the results of recent drug trials and, if confirmed, may guide future drug development.

Glycogen synthase kinase-3beta and tau genes interact in Alzheimer's disease

OBJECTIVE

We examined the epistatic effect between haplotypes of glycogen synthase kinase-3beta (GSK3B) gene and microtubule-associated protein Tau (MAPT) gene in Alzheimer's disease (AD).

METHODS

A genetic association study of three AD cohorts was made. Linear regression analyses were used to examine effects of MAPT polymorphisms on gene expression and alternative splicing. beta-Catenin levels and signaling were determined using Western blot and luciferase reporter assays in cells transfected with a combination of GSK3B and MAPT complementary DNA.

RESULTS

Consistent interaction between GSK3B and MAPT genes in three late-onset AD cohorts was observed, with the GSK3B haplotype (T-T) significantly increasing the risk for AD in individuals with at least one H2 haplotype (odds ratio, 1.68-2.33; p = 0.005-0.036). The GSK3B haplotype was significantly protective in the Chinese cohort (odds ratio, 0.33; p = 0.016), after adjusting for the effect of age and sex. There are significant differences in in vivo transcriptional efficiency between the two MAPT haplotypes (H1 and H2) as determined by measurement of cerebellar transcripts (p < 0.001). Overexpression of either MAPT or GSK3B resulted in decreased beta-catenin levels compared with a control vector (p < 0.001). Conversely, cotransfection of both of these molecules increased beta-catenin signaling.

INTERPRETATION

Our genetic and biochemical analyses have identified a novel interaction between Tau and GSK-3beta in late-onset AD causative factors. Our data are consistent with an epistatic model of interaction where discordant levels of GSK3B and MAPT gene expression can lead to altered beta-catenin levels and pathogenicity.

The GSK3 hypothesis of Alzheimer's disease

Glycogen synthase kinase 3 (GSK3) is a constitutively active, proline-directed serine/threonine kinase that plays a part in a number of physiological processes ranging from glycogen metabolism to gene transcription. GSK3 also plays a pivotal and central role in the pathogenesis of both sporadic and familial forms of Alzheimer's disease (AD), an observation that has led us to coin the ‘GSK3 hypothesis of AD’. According to this hypothesis, over-activity of GSK3 accounts for memory impairment, tau hyper-phosphorylation, increased β-amyloid production and local plaque-associated microglial-mediated inflammatory responses; all of which are hallmark characteristics of AD. If our ‘GSK3 hypothesis of AD’ is substantiated and GSK3 is indeed a causal mediator of AD then inhibitors of GSK3 would provide a novel avenue for therapeutic intervention in this devastating disorder.

Response to lithium augmentation in depression is associated with the glycogen synthase kinase 3-beta -50T/C single nucleotide polymorphism

BACKGROUND

Glycogen synthase kinase 3-beta (GSK3B) is a serine/threonine kinase which is directly inhibited by lithium. A -50T/C single nucleotide polymorphism (SNP) localized within the promoter region of the GSK3B gene has previously been shown to be associated with response to lithium prophylaxis in bipolar disorder. This study investigates the association of the GSK3B -50T/C SNP and response to lithium augmentation in acutely depressed antidepressant nonresponders.

METHODS

Eighty-one patients who had not responded to at least one adequate trial of antidepressant monotherapy underwent a standardized trial of lithium augmentation for up to 8 weeks. We genotyped for the GSK3B -50T/C SNP using polymerase chain reaction and restriction fragment length polymorphism methods and investigated the association with remission.

RESULTS

The allele frequencies in our sample were CC 14.8%, CT 48.2% and TT 37% (no deviation from the Hardy-Weinberg equilibrium). Carriers of the C-allele of the -50T/C SNP showed a significantly better response to lithium augmentation (hazard ratio: 2.70, p = .007), with a mean remission rate of 56.25% after 4 weeks compared to 31% in patients with the TT-genotype (chi(2) = 4.1; p = .04).

CONCLUSIONS

Our results support the finding of recent studies demonstrating a superior response of C-allele carriers with bipolar disorder to lithium prophylaxis.

The ups and downs of Wnt signaling in prevalent neurological disorders

In order to function properly, the brain must be wired correctly during critical periods in early development. Mistakes in this process are hypothesized to occur in disorders like autism and schizophrenia. Later in life, signaling pathways are essential in maintaining proper communication between neuronal and non-neuronal cells, and disrupting this balance may result in disorders like Alzheimer's disease. The Wnt/beta-catenin pathway has a well-established role in cancer. Here, we review recent evidence showing the involvement of Wnt/beta-catenin signaling in neurodevelopment as well as in neurodegenerative diseases. We suggest that the onset/development of such pathological conditions may involve the additive effect of genetic variation within Wnt signaling components and of molecules that modulate the activity of this signaling cascade.

β-Amyloid peptide toxicity in organotypic hippocampal slice culture involves Akt/PKB, GSK-3β, and PTEN

In the present study we investigated the toxicity induced by exposing organotypic slice culture to beta-amyloid peptide 25-35 (25microM) for 1, 3, 6, 12, 24 and 48h. To elucidate a mechanism involved in its toxicity, we studied the PI3-K cell signaling pathway, particularly Akt/PKB, GSK-3beta, and PTEN proteins. Cell death was quantified by propidium iodide uptake and proteins were analyzed by immunoblotting. Our results showed a significant cell death after 48h of beta-amyloid 25-35 peptide exposition. The exposition of cultures to beta-amyloid peptide resulted in an increase in the phosphorylation state of Akt and GSK-3beta proteins after 6h, followed by a decrease of the phosphorylation state of these proteins after 12h of exposition. However, after 24h of peptide treatment, the phosphorylation of GSK-3beta presented a new increase while the phosphorylation of Akt remained down. The immunocontent of the PTEN protein, an indirect Akt phosphatase, increased after 24 and 48h of beta-amyloid exposition. These results suggest an involvement of Akt dephosphorylation/inactivation in the toxicity induced by the beta-amyloid 25-35 peptide in organotypic slice hippocampal culture, probably induced by increasing PTEN immunocontent. Taken together, our results provide more information about the molecular mechanisms involved on beta-amyloid peptide toxicity.