Glycogen synthase kinase-3 (GSK3) in psychiatric diseases and therapeutic interventions

Glycogen synthase kinase 3: a point of integration in Alzheimer's disease and a therapeutic target?

Glycogen synthase kinase 3 (GSK3) has been implicated in neurological disorders; therefore, it is not surprising that there has been an increased focus towards developing therapies directed to this kinase. Unfortunately, these current therapies have not taken into consideration the physiological role of GSK3 in crucial events like synaptic plasticity. With this in mind we will discuss the relationship of synaptic plasticity with GSK3 and tau protein and their role as potential targets for the development of therapeutic strategies. Finally, we will provide perspectives in developing a cocktail therapy for Alzheimer's treatment.

Inhibition of GSK3 attenuates amphetamine-induced hyperactivity and sensitization in the mouse

Glycogen synthase kinase 3 (GSK3) is implicated in mediating dopamine-dependent behaviors. Previous studies have demonstrated the ability of amphetamine, which increases extracellular dopamine levels and influences behavior, to regulate the activity of GSK3. This study used valproic acid and the selective GSK3 inhibitor, SB 216763, to examine the role of GSK3 in amphetamine-induced hyperactivity and the development of sensitized stereotypic behavior. Pretreatment with valproic acid (50-300 mg/kg, i.p.) or SB 216763 (2.5-5 mg/kg, i.p.) prior to amphetamine (2 mg/kg, i.p.) significantly reduced amphetamineinduced ambulation and stereotypy. To assess the development of sensitization to the stereotypic effects of amphetamine, mice were pretreated daily with valproic acid (300 mg/kg) or SB 216763 (5 mg/kg) prior to amphetamine (2 mg/kg) for 5 days. Upon amphetamine challenge (1 mg/kg) 7 days later, mice pretreated with valproate or SB 216763 showed a significant attenuation of amphetamine-induced sensitization of stereotypy. To determine whether regulation of GSK3 activity was associated with attenuation of acute amphetamine-induced hyperactivity by valproic acid, valproate (300 mg/kg) or vehicle was injected prior to amphetamine (2 mg/kg) or saline and brain tissue obtained. Analysis of the levels of phospho-GSK3α and β by immunoblot indicated that valproate increased phosphorylation of ser²¹-GSK3α in the frontal cortex, as well as ser⁹-GSK3β in the frontal cortex and caudate putamen of amphetamine-injected mice. These data support a role for GSK3 in acute amphetamine-induced hyperactivity and the development of sensitization to amphetamine-induced stereotypy.

Involvement of PI3K, GSK-3β and PPARγ in the antidepressant-like effect of folic acid in the forced swimming test in mice

Preclinical and clinical studies indicate that deficiency in folic acid plays a role in the pathophysiology of depression. Considering that alterations in the signaling pathways that regulate neuroplasticity and cellular survival are implicated in depressive disorders, the present study investigated the involvement of the phosphoinositide 3-kinase (PI3K), glycogen synthase kinase-3 (GSK-3β), and peroxisome proliferator-activated receptor-γ (PPARγ) in the antidepressant-like effect of folic acid in the forced swimming test (FST). The intracerebroventricular (i.c.v.) pre-treatment of mice with LY294002 (10 nmol/site, a PI3K inhibitor) or GW-9662 (1 µg/site, a PPARγ antagonist) prevented the antidepressant-like effect of folic acid (50 mg/kg, p.o.) in the FST. In addition, the administration of subeffective doses of the selective GSK-3β inhibitor, AR-A014418 (3 mg/kg, i.p.), a non-selective GSK-3β inhibitor, lithium chloride (10 mg/kg, p.o) or a PPARγ agonist, rosiglitazone (1 µg/site, i.c.v.) in combination with a subeffective dose of folic acid (10 mg/kg, p.o.) significantly reduced the immobility time in the FST as compared with either drug alone, without altering the locomotor activity. These results indicate that the antidepressant-like effect of folic acid in the FST might be dependent on inhibition of GSK-3β and activation of PPARγ, reinforcing the notion that these are important targets for antidepressant activity.

Altered regulation of tau phosphorylation in a mouse model of down syndrome aging

Down syndrome (DS) results from trisomy of human chromosome 21 (Hsa21) and is associated with an increased risk of Alzheimer's disease (AD). Here, using the unique transchromosomic Tc1 mouse model of DS we investigate the influence of trisomy of Hsa21 on the protein tau, which is hyperphosphorylated in Alzheimer's disease. We show that in old, but not young, Tc1 mice increased phosphorylation of tau occurs at a site suggested to be targeted by the Hsa21 encoded kinase, dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A). We show that DYRK1A is upregulated in young and old Tc1 mice, but that young trisomic mice may be protected from accumulating aberrantly phosphorylated tau. We observe that the key tau kinase, glycogen synthase kinase3-β (GSK-3β) is aberrantly phosphorylated at an inhibitory site in the aged Tc1 brain which may reduce total glycogen synthase kinase3-β activity. It is possible that a similar mechanism may also occur in people with DS.

Protein levels of β-catenin and activation state of glycogen synthase kinase-3β in major depression. A study with postmortem prefrontal cortex

BACKGROUND

The Wnt/GSK3β signaling pathway was implicated in mood disorders. Beta-catenin is a protein targeted by this signaling axis. We aimed to examine whether there is an abnormality in this signaling axis in major depression.

METHODS

Postmortem brains from 20 depressed and 20 non-depressed subjects were used. In both groups, suicide and non-suicide were included in equal number. Protein levels of β-catenin, tGSK3β and ser(9)-pGSK3β were determined in prefrontal cortex.

RESULTS

ANOVA yielded significant variations between groups in β-catenin (F(3,36)=19.5; p<0.001) and pGSK3β protein (F(3,36)=14.3; p<0.001) and in tGSK3β-to-pGSK3β ratio (F(3,36)=10.9; p<0.001). Fisher tests showed decrease in both groups of MDD and MDD with suicide (MDD+S) for β-catenin (p<0.001) and pGSK3β levels (p<0.001) respectively. The tGSK3β-to-pGSK3β ratio was increased in MDD and MDD+S subjects (p<0.001). A negative correlation was observed between β-catenin levels and the activation state of the GSK3β (r2=0.358; p<0.005).

LIMITATIONS

The sample was small and only a fraction of s(9)-pGSK3β, albeit significant, was used and; the mood state at the time of death was unknown.

CONCLUSIONS

The study observed a dysregulation of Wnt/GSK3β signaling associated with a lifetime of major depression. The study may have relevance in further development of drugs based on GSK3β inhibition.

Adenomatous polyposis coli (APC) regulates multiple signaling pathways by enhancing glycogen synthase kinase-3 (GSK-3) activity

Glycogen synthase kinase-3 (GSK-3) is essential for many signaling pathways and cellular processes. As Adenomatous Polyposis Coli (APC) functions in many of the same processes, we investigated a role for APC in the regulation of GSK-3-dependent signaling. We find that APC directly enhances GSK-3 activity. Furthermore, knockdown of APC mimics inhibition of GSK-3 by reducing phosphorylation of glycogen synthase and by activating mTOR, revealing novel roles for APC in the regulation of these enzymes. Wnt signaling inhibits GSK-3 through an unknown mechanism, and this results in both stabilization of β-catenin and activation of mTOR. We therefore hypothesized that Wnts may regulate GSK-3 by disrupting the interaction between APC and the Axin-GSK-3 complex. We find that Wnts rapidly induce APC dissociation from Axin, correlating with β-catenin stabilization. Furthermore, Axin interaction with the Wnt co-receptor LRP6 causes APC dissociation from Axin. We propose that APC regulates multiple signaling pathways by enhancing GSK-3 activity, and that Wnts induce APC dissociation from Axin to reduce GSK-3 activity and activate downstream signaling. APC regulation of GSK-3 also provides a novel mechanism for Wnt regulation of multiple downstream effectors, including β-catenin and mTOR.

Antidepressant-like effect of extract from Polygala paniculata: involvement of the monoaminergic systems

CONTEXT

Polygala paniculata Linnaeus (Polygalaceae) has shown neuroprotective effects, but there is no report about its antidepressant potential.

OBJECTIVE

The antidepressant-like effect of the hydroalcoholic extract from P. paniculata and some of the possible mechanisms involved in this effect were investigated in forced swimming test (FST).

MATERIALS AND METHODS

Mice received extract by oral route and were submitted to FST and open-field test. Animals were forced to swim and the total immobility time was registered (6-min period). A reduction in the immobility time is considered an antidepressant-like effect. In order to investigate the involvement of the monoaminergic systems, mice were treated with pharmacological antagonists before administration of the extract.

RESULTS

The acute administration of the hydroalcoholic extract from P. paniculata produced an antidepressant-like effect, since it significantly reduced the immobility time in FST (0.01-30 mg/kg) as compared to control group, without changing locomotor activity. Pretreatment of mice with yohimbine (1 mg/kg, i.p., α₂-adrenoceptor antagonist), propranolol (1 mg/kg, i.p., β-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., dopamine D₁ receptor antagonist) or sulpiride (50 mg/kg, i.p., dopamine D₂ receptor antagonist) prevented the antidepressant-like effect of the extract in FST (30 mg/kg). Moreover, ketanserin (5 mg/kg, i.p., preferential 5-HT(2A) receptor antagonist) enhanced the effect of the extract in FST.

DISCUSSION AND CONCLUSION

The results of the present study indicate that the extract from P. paniculata has an antidepressant-like action that is likely mediated by an interaction with the serotonergic (5-HT2A receptors), noradrenergic (α₂ and β-receptor) and dopaminergic (D₁ and D₂ receptors) systems.

GSK-3 Mouse Models to Study Neuronal Apoptosis and Neurodegeneration

Increased GSK-3 activity is believed to contribute to the etiology of chronic disorders like Alzheimer’s disease (AD), schizophrenia, diabetes, and some types of cancer, thus supporting therapeutic potential of GSK-3 inhibitors. Numerous mouse models with modified GSK-3 have been generated in order to study the physiology of GSK-3, its implication in diverse pathologies and the potential effect of GSK-3 inhibitors. In this review we have focused on the relevance of these mouse models for the study of the role of GSK-3 in apoptosis. GSK-3 is involved in two apoptotic pathways, intrinsic and extrinsic pathways, and plays opposite roles depending on the apoptotic signaling process that is activated. It promotes cell death when acting through intrinsic pathway and plays an anti-apoptotic role if the extrinsic pathway is occurring. It is important to dissect this duality since, among the diseases in which GSK-3 is involved, excessive cell death is crucial in some illnesses like neurodegenerative diseases, while a deficient apoptosis is occurring in others such as cancer or autoimmune diseases. The clinical application of a classical GSK-3 inhibitor, lithium, is limited by its toxic consequences, including motor side effects. Recently, the mechanism leading to activation of apoptosis following chronic lithium administration has been described. Understanding this mechanism could help to minimize side effects and to improve application of GSK-3 inhibitors to the treatment of AD and to extend the application to other diseases.

Functional significance of glycogen synthase kinase-3 regulation by serotonin

Serotonin modulates brain physiology and behavior and has major roles in brain diseases involving abnormal mood and cognition. Enhancing brain serotonin has been found to regulate glycogen synthase Kinase-3 (GSK3), but the signaling mechanism and functional significance of this regulation remain to be determined. In this study, we tested the signaling mechanism mediating 5-HT1A receptor-regulated GSK3 in the hippocampus. Using mutant GSK3 knock-in mice, we also tested the role of GSK3 in the behavioral effects of 5-HT1A receptors and the serotonin reuptake inhibitor fluoxetine. The results showed that activation of 5-HT1A receptors by 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) increased phosphorylation of the N-terminal serine of both GSK3α and GSK3β in several areas of the hippocampus. The effect of 8-OH-DPAT was accompanied by an increase in the active phosphorylation of Akt, and was blocked by LY294002, an inhibitor of phosphoinositide 3-kinases (PI3K). Phosphorylation of GSK3β, but not GSK3α, was necessary for 5-HT1A receptors to suppress the hippocampus-associated contextual fear learning. Furthermore, acute fluoxetine treatment up-regulated both phospho-Ser21-GSK3α and phospho-Ser9-GSK3β in the hippocampus. Blocking phosphorylation of GSK3α and GSK3β diminished the anti-immobility effect of fluoxetine treatment in the forced swim test, wherein the effect of GSK3β was more prominent. These results together suggest that PI3K/Akt is a signaling mechanism mediating the GSK3-regulating effect of 5-HT1A receptors in the hippocampus, and regulation of GSK3 is an important intermediate signaling process in the behavioral functions of 5-HT1A receptors and fluoxetine.

GSK-3 as a Target for Lithium-Induced Neuroprotection Against Excitotoxicity in Neuronal Cultures and Animal Models of Ischemic Stroke

The mood stabilizer lithium inhibits glycogen synthase kinase-3 (GSK-3) directly or indirectly by enhancing serine phosphorylation of both α and β isoforms. Lithium robustly protected primary brain neurons from glutamate-induced excitotoxicity; these actions were mimicked by other GSK-3 inhibitors or silencing/inhibiting GSK-3α and/or β isoforms. Lithium rapidly activated Akt to enhance GSK-3 serine phosphorylation and to block glutamate-induced Akt inactivation. Lithium also up-regulated Bcl-2 and suppressed glutamate-induced p53 and Bax. Induction of brain-derived neurotrophic factor (BDNF) was required for lithium’s neuroprotection to occur. BDNF promoter IV was activated by GSK-3 inhibition using lithium or other drugs, or through gene silencing/inactivation of either isoform. Further, lithium’s neuroprotective effects were associated with inhibition of NMDA receptor-mediated calcium influx and down-stream signaling. In rodent ischemic models, post-insult treatment with lithium decreased infarct volume, ameliorated neurological deficits, and improved functional recovery. Up-regulation of heat-shock protein 70 and Bcl-2 as well as down-regulation of p53 likely contributed to lithium’s protective effects. Delayed treatment with lithium improved functional MRI responses, which was accompanied by enhanced angiogenesis. Two GSK-3-regulated pro-angiogenic factors, matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor were induced by lithium. Finally, lithium promoted migration of mesenchymal stem cells (MSCs) by up-regulation of MMP-9 through GSK-3β inhibition. Notably, transplantation of lithium-primed MSCs into ischemic rats enhanced MSC migration to the injured brain regions and improved the neurological performance. Several other GSK-3 inhibitors have also been reported to be beneficial in rodent ischemic models. Together, GSK-3 inhibition is a rational strategy to combat ischemic stroke and other excitotoxicity-related brain disorders.

The impact of glycogen synthase kinase 3β gene on psychotic mania in bipolar disorder patients

OBJECTIVE

The aim of this study was to examine the relationships between glycogen synthase 3β gene polymorphisms and bipolar I disorder, manic in a Korean sample.

METHODS

Patients with bipolar disorder (n=118) and a control group (n=158) were assessed by genotyping for GSK3β single nucleotide polymorphisms (SNPs) -1727A/T and -50C/T. The patients were divided into two groups according to the presence of psychotic symptoms (psychotic mania, n=92; non-psychotic mania, n=26) and also divided based on gender and age of onset. The severity of symptoms was measured using the Young Mania Rating Scale (YMRS) and the Brief Psychiatric Rating Scale (BPRS).

RESULTS

There were no significant differences in the genotype distributions or allelic frequencies of GSK3β polymorphisms and gender between patients with bipolar disorder and a normal control group. According to haplotype analysis, there was no association between these two groups. However, analysis of the age of onset of bipolar disorder revealed significant differences in genotype and allele distributions among the patients. Patients who were homozygous for the wild-type variant (TT) had an older age of onset than carriers of the mutant allele (A/A: 27.4±9.1; A/T: 30.1±11.8; T/T: 42.3±19.9; p=0.034). We detected differences in allele frequencies of the GSK3β -1727A/T polymorphism between the psychotic mania group and the non-psychotic mania group.

CONCLUSION

This study suggests that GSK3β polymorphisms are not associated with bipolar disorder. However, the GSK3β SNP -1727A/T is associated with age of onset and presence of psychotic symptoms in bipolar disorder.

Inhibition of glycogen synthase kinase-3 enhances the differentiation and reduces the proliferation of adult human olfactory epithelium neural precursors

The olfactory epithelium (OE) contains neural precursor cells which can be easily harvested from a minimally invasive nasal biopsy, making them a valuable cell source to study human neural cell lineages in health and disease. Glycogen synthase kinase-3 (GSK-3) has been implicated in the etiology and treatment of neuropsychiatric disorders and also in the regulation of murine neural precursor cell fate in vitro and in vivo. In this study, we examined the impact of decreased GSK-3 activity on the fate of adult human OE neural precursors in vitro. GSK-3 inhibition was achieved using ATP-competitive (6-bromoindirubin-3'-oxime and CHIR99021) or substrate-competitive (TAT-eIF2B) inhibitors to eliminate potential confounding effects on cell fate due to off-target kinase inhibition. GSK-3 inhibitors decreased the number of neural precursor cells in OE cell cultures through a reduction in proliferation. Decreased proliferation was not associated with a reduction in cell survival but was accompanied by a reduction in nestin expression and a substantial increase in the expression of the neuronal differentiation markers MAP1B and neurofilament (NF-M) after 10 days in culture. Taken together, these results suggest that GSK-3 inhibition promotes the early stages of neuronal differentiation in cultures of adult human neural precursors and provide insights into the mechanisms by which alterations in GSK-3 signaling affect adult human neurogenesis, a cellular process strongly suspected to play a role in the etiology of neuropsychiatric disorders.

Lithium ameliorates phenotypic deficits in a mouse model of fragile X syndrome

As our understanding of the underlying defects in fragile X syndrome (FXS) increases so does the potential for development of treatments aimed at modulating the defects and ameliorating the constellation of symptoms seen in patients. Symptoms of FXS include cognitive disability, hyperactivity, autistic behaviour, seizures and learning deficits. Lithium is a drug used clinically to treat bipolar disorder, and it has been used to treat mood dysregulation in individuals with FXS. We examined whether dietary lithium would alter behavioural and morphological abnormalities in fmr1 knockout (KO) mice. We studied wild-type (WT) and KO mice untreated (control chow) or treated with lithium (0.3% lithium-carbonate-containing chow) commenced at weaning and maintained throughout the experiment. At age 8-12 wk, mice were subjected to the following behavioural tests: open field, social interaction, elevated plus maze, elevated zero maze and passive avoidance. At 13 wk, brains were prepared for Golgi staining and analysis of dendritic spine morphology in medial prefrontal cortex. We found that compared to untreated WT, untreated KO mice were hyperactive and had reduced anxiety, impaired social interactions, and deficits on a learning test. Dendritic spines in medial prefrontal cortex were longer and increased in number. Lithium treatment ameliorated the hyperactivity and reversed impaired social interaction and deficits on the learning test. Lithium treatment also partially normalized general anxiety levels and dendritic spine morphology. Our findings and those from other laboratories on the efficacy of lithium treatment in animal models support further studies in patients with FXS.

Genetic inactivation of GSK3α rescues spine deficits in Disc1-L100P mutant mice

Disrupted-in-Schizophrenia 1 (DISC1), a strong candidate gene for schizophrenia and other mental disorders, regulates neurodevelopmental processes including neurogenesis, neuronal migration, neurite outgrowth and spine development. Glycogen synthase kinase-3 (GSK3) directly interacts with DISC1 and also plays a role in neurodevelopment. Recently, our group showed that the Disc1-L100P mutant protein has reduced interaction with both GSK3α and β. Genetic and pharmacological inhibition of GSK3 activity rescued behavioral abnormalities in Disc1-L100P mutant mice. However, the cellular mechanisms mediating these effects of GSK3 inhibition in Disc1 mutant mice remain unclear. We sought to investigate the effects of genetic inactivation of GSK3α on frontal cortical neuron morphology in Disc1 L100P mutant mice using Golgi staining. We found a significant decrease in dendritic length and surface area in Disc1-L100P, GSK3α null and L100P/GSK3α double mutants. Dendritic spine density was significantly reduced only in Disc1-L100P and L100P/GSK3α +/- mice when compared to wild-type littermates. There was no difference in dendritic arborization between the various genotypes. No significant rescue in dendritic length and surface area was observed in L100P/GSK3α mutants versus L100P mice, but spine density in L100P/GSK3α mice was comparable to wild-type. Neurite outgrowth and spine development abnormalities induced by Disc1 mutation may be partially corrected through GSK3α inactivation, which also normalizes behavior. However, many of the other dendritic abnormalities in the Disc1-L100P mutant mice were not corrected by GSK3α inactivation, suggesting that only some of the anatomical defects have observable behavioral effects. These findings suggest novel treatment approaches for schizophrenia, and identify a histological read-out for testing other therapeutic interventions.

α-Tocopherol impairs 7-ketocholesterol-induced caspase-3-dependent apoptosis involving GSK-3 activation and Mcl-1 degradation on 158N murine oligodendrocytes

In important and severe neurodegenerative pathologies, 7-ketocholesterol, mainly resulting from cholesterol autoxidation, may contribute to dys- or demyelination processes. On various cell types, 7-ketocholesterol has often been shown to induce a complex mode of cell death by apoptosis associated with phospholipidosis. On 158N murine oligodendrocytes treated with 7-ketocholesterol (20 μg/mL corresponding to 50 μM, 24-48 h), the induction of a mode of cell death by apoptosis characterised by the occurrence of cells with condensed and/or fragmented nuclei, caspase activation (including caspase-3) and internucleosomal DNA fragmentation was observed. It was associated with a loss of transmembrane mitochondrial potential (ΔΨm) measured with JC-1, with a dephosphorylation of Akt and GSK3 (especially GSK3β), and with degradation of Mcl-1. With α-tocopherol (400 μM), which was capable of counteracting 7-ketocholesterol-induced apoptosis, Akt and GSK3β dephosphorylation were inhibited as well as Mcl-1 degradation. These data underline that the potential protective effects of α-tocopherol against 7-ketocholesterol-induced apoptosis do not depend on the cell line considered, and that the cascade of events (Akt/GSK3β/Mcl-1) constitutes a link between 7-ketocholesterol-induced cytoplasmic membrane dysfunctions and mitochondrial depolarisation leading to apoptosis.

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.

Group II metabotropic glutamate receptor agonist ameliorates MK801-induced dysfunction of NMDA receptors via the Akt/GSK-3β pathway in adult rat prefrontal cortex

Pharmacological intervention targeting mGluRs has emerged as a potential treatment for schizophrenia, whereas the mechanisms involved remain elusive. We explored the antipsychotic effects of an mGluR2/3 agonist in the MK-801 model of schizophrenia in the rat prefrontal cortex. We found that the mGluR2/3 agonist LY379268 effectively recovered the disrupted expression of NMDA receptors induced by MK-801 administration. This effect was attributable to the direct regulatory action of LY379268 on NMDA receptors via activation of the Akt/GSK-3β signaling pathway. As occurs with the antipsychotic drug clozapine, acute treatment with LY379268 significantly increased the expression and phosphorylation of NMDA receptors, as well as Akt and GSK-3β. Physiologically, LY379268 significantly enhanced NMDA-induced current in prefrontal neurons and a GSK-3β inhibitor occluded this effect. In contrast to the widely proposed mechanism of modulating presynaptic glutamate release, our results strongly argue that mGluR2/3 agonists modulate the function of NMDA receptors through postsynaptic actions and reverse the MK-801-induced NMDA dysfunction via the Akt/GSK-3β pathway. This study provides novel evidence for postsynaptic mechanisms of mGluR2/3 in regulation of NMDA receptors and presents useful insights into the mechanistic actions of mGluR2/3 agonists as potential antipsychotic agents for treating schizophrenia.

The role of zinc in neurodegenerative inflammatory pathways in depression

According to new hypothesis, depression is characterized by decreased neurogenesis and enhanced neurodegeneration which, in part, may be caused by inflammatory processes. There is much evidence indicating that depression, age-related changes often associated with impaired brain function and cognitive performances or neurodegenerative processes could be related to dysfunctions affecting the zinc ion availability. Clinical studies revealed that depression is accompanied by serum hypozincemia, which can be normalized by successful antidepressant treatment. In patients with major depression, a low zinc serum level was correlated with an increase in the activation of markers of the immune system, suggesting that this effect may result in part from a depression-related alteration in the immune-inflammatory system. Moreover, a preliminary clinical study demonstrated the benefit of zinc supplementation in antidepressant therapy in both treatment non-resistant and resistant patients. In the preclinical study, the antidepressant activity of zinc was observed in the majority of rodent tests and models of depression and revealed a causative role for zinc deficiency in the induction of depressive-like symptoms, the reduction of neurogenesis and neuronal survival or impaired learning and memory ability. This paper provides an overview of the clinical and experimental evidence that implicates the role of zinc in the pathophysiology and therapy of depression within the context of the inflammatory and neurodegenerative hypothesis of this disease.

Synaptic Wnt signaling-a contributor to major psychiatric disorders?

Wnt signaling is a key pathway that helps organize development of the nervous system. It influences cell proliferation, cell fate, and cell migration in the developing nervous system, as well as axon guidance, dendrite development, and synapse formation. Given this wide range of roles, dysregulation of Wnt signaling could have any number of deleterious effects on neural development and thereby contribute in many different ways to the pathogenesis of neurodevelopmental disorders. Some major psychiatric disorders, including schizophrenia, bipolar disorder, and autism spectrum disorders, are coming to be understood as subtle dysregulations of nervous system development, particularly of synapse formation and maintenance. This review will therefore touch on the importance of Wnt signaling to neurodevelopment generally, while focusing on accumulating evidence for a synaptic role of Wnt signaling. These observations will be discussed in the context of current understanding of the neurodevelopmental bases of major psychiatric diseases, spotlighting schizophrenia, bipolar disorder, and autism spectrum disorder. In short, this review will focus on the potential role of synapse formation and maintenance in major psychiatric disorders and summarize evidence that defective Wnt signaling could contribute to their pathogenesis via effects on these late neural differentiation processes.

Regulation of PI3K/Akt signaling by N-desmethylclozapine through activation of δ-opioid receptor

We have previously reported that N-desmethylclozapine (NDMC), a major clozapine metabolite, acts as a δ-opioid receptor agonist. Here, we show that in different cellular systems NDMC regulates protein kinase B/Akt (Akt) signaling through the activation of δ-opioid receptors. In Chinese hamster ovary cells transfected with the human δ-opioid receptor (CHO/DOR), NDMC induced a time- and concentration-dependent phosphorylation of Akt at Thr308 and glycogen synthase kinase-3β (GSK-3β) at Ser9 and these effects were fully blocked by the δ-opioid receptor antagonist naltrindole. NDMC-induced Akt and GSK-3β phosphorylations were completely prevented by pertussis toxin, the Src tyrosine kinase inhibitor PP2 and the selective insulin-like growth factor-I (IGF-I) receptor tyrosine kinase inhibitor tyrphostin AG 1024. NDMC stimulated IGF-I receptor β subunit tyrosine phosphorylation and this effect was prevented by either naltrindole or PP2. Blockade of phosphatidylinositol 3-kinase (PI3K) α, but not PI3Kγ, suppressed NDMC-induced Akt and GSK-3β phosphorylation, whereas inhibition of Akt curtailed the stimulation of GSK-3β phosphorylation. In rat nucleus accumbens, NDMC induced Akt and GSK-3β phosphorylation either in vitro or in vivo and these effects were prevented by naltrindole. NDMC also regulated Akt and GSK-3β phosphorylation through δ-opioid receptors in NG108-15 cells. In these cells NDMC counteracted oxidative stress-induced apoptosis and the effect was lost following PI3K inhibition. These data demonstrate that in different cell systems NDMC can stimulate Akt signaling by activating Gi/Go-coupled δ-opioid receptors, which, at least in CHO/DOR cells, regulate PI3Kα through Src-dependent transactivation of the IGF-I receptor, and indicate that through this mechanism NDMC can exert neuroprotective effects.

Genetic and pharmacological evidence for schizophrenia-related Disc1 interaction with GSK-3

Recent studies have identified disrupted-in-schizophrenia-1 (DISC1) as a strong genetic risk factor associated with schizophrenia. Previously, we have reported that a mutation in the second exon of the DISC1 gene [leucine to proline at amino acid position 100, L100P] leads to the development of schizophrenia-related behaviors in mice. Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase that interacts with the N-terminal region of DISC1 (aa 1-220) and has been implicated as an important downstream component in the etiology of schizophrenia. Here, for the first time, we show that pharmacological and genetic inactivation of GSK-3 reverse prepulse inhibition and latent inhibition deficits as well as normalizing the hyperactivity of Disc1-L100P mutants. In parallel to these observations, interaction between DISC1 and GSK-3α and β is reduced in Disc1-L100P mutants. Our data provide genetic, biochemical, and behavioral evidence for a molecular link between DISC1 and GSK-3 in relation to psychopathology and highlights the value of missense mutations in dissecting the underlying and complex molecular mechanisms of neurological disorders.

Platelet GSK3B activity in patients with late-life depression: marker of depressive episode severity and cognitive impairment?

OBJECTIVE

Increased GSK3B activity has been reported as a state marker of major affective episodes in patients with depression and bipolar disorder. No study so far has addressed GSK3B activity in late-life depression. The aims of the present study were to determine GSK3B activity in platelets of elderly patients with major depression, and the association between GSK3B activity and the severity of depressive symptoms and cognitive impairment.

METHODS

Forty drug-free elderly patients with major depressive episode were compared to healthy older adults (n = 13). Severity of the depressive episode and current cognitive state were determined by the Hamilton Depression Scale (HAM-D) and the Cambridge Cognitive Test (CAMCOG), respectively. Total- and ser-9-phosphorylated GSK3B (tGSK3B and pGSK3B) were determined in platelets by enzyme immunometric assays (EIA). GSK3B activity was indirectly inferred by the GSK3B ratio (i.e. pGSK3B/tGSK3B).

RESULTS

Elderly depressed patients had significantly lower pGSK3B levels (P = 0.03) and GSK3B ratio (P = 0.03), indicating higher GSK3B activity. Higher GSK3B activity were observed in patients with severe depressive episode (HAM-D scores >22, P = 0.03) and with cognitive impairment (CAMCOG scores <86, P = 0.01).

CONCLUSION

The present findings provide additional evidence of the involvement of GSK3B in the pathophysiology of late-life major depression. Higher GSK3B activity may be more relevant in those patients with more severe depressive symptoms and cognitive impairment.

Synergistic interactions between PDE4B and GSK-3: DISC1 mutant mice

Disrupted-In-Schizophrenia-1 (DISC1) is a strong genetic risk factor associated with psychiatric disorders. Two distinct mutations in the second exon of the DISC1 gene (Q31L and L100P) lead to either depression- or schizophrenia-like behavior in mice. Both phosphodiesterase-4B (PDE4B) and glycogen synthase kinase-3 (GSK-3) have common binding sites on N-terminal region of DISC1 and are implicated into etiology of schizophrenia and depression. It is not known if PDE4B and GSK-3 could converge signals in the cell via DISC1 at the same time. The purpose of the present study was to assess whether rolipram (PDE4 inhibitor) might synergize with TDZD-8 (GSK-3 blocker) to produce antipsychotic effects at low doses on the DISC1-L100P genetic model. Indeed, combined treatment of DISC1-L100P mice with rolipram (0.1 mg/kg) and TDZD-8 (2.5 mg/kg) in sub-threshold doses corrected their Pre-Pulse Inhibition (PPI) deficit and hyperactivity, without any side effects at these doses. We have suggested that rolipram-induced increase of cAMP level might influence GSK-3 function and, hence the efficacy of TDZD-8. Our second goal was to estimate how DISC1-Q31L with reduced PDE4B activity, and therefore mimicking rolipram-induced conditions, could alter pharmacological response to TDZD-8, GSK-3 activity and its interaction with DISC1. DISC1-Q31L mutants showed increased sensitivity to GSK-3 inhibitor compare to DISC1-L100P mice. TDZD-8 (2.5 mg/kg) was able to correct PPI deficit, reduce immobility in the forced swim test (FST) and increased social motivation/novelty. In parallel, biochemical analysis revealed significantly reduced binding of GSK-3 to the mutated DISC1-Q31L and increased enzymatic activity of GSK-3. Taken together, genetic variations in DISC1 influence formation of biochemical complex with PDE4 and GSK-3 and strength the possibility of synergistic interactions between these proteins.

The involvement of GABA(A) receptor in the molecular mechanisms of combined selective serotonin reuptake inhibitor-antipsychotic treatment

There is evidence that combining selective serotonin reuptake inhibitor (SSRI) antidepressant and antipsychotic drugs may improve negative symptoms in schizophrenia and resistant symptoms in obsessive-compulsive and affective disorders. To examine the mechanism of action of this treatment we investigated the molecular modulation of γ-aminobutyric acid-A (GABA(A)) receptor components and biochemical pathways associated with GABA(A) receptor function following administration of the SSRI fluvoxamine (Flu) combined with the first-generation antipsychotic haloperidol (Hal) and compared it to the individual drugs and the atypical antipsychotic clozapine (Clz). We analysed prefrontal cortices of Sprague-Dawley rats injected intraperitoneally (i.p.) with the combination of Flu (10 mg/kg) and Hal (1 mg/kg), each drug alone, or Clz (10 mg/kg) after 30 min and 1 h. We found that haloperidol plus fluvoxamine (Hal-Flu) co-administration, and Clz, decreased the level of GABAAβ2/3 receptor subunit in the cytosolic fraction, and increased it in the membrane compartment in rat PFC. Flu or Hal alone did not produce changes in GABAAβ2/3 receptor protein expression. Additionally, Hal-Flu and Clz regulated molecular signalling pathways that modulate GABA(A) receptor function, including protein kinase C (PKC) and extracellular signal-regulated kinase-2 (ERK2). In primary cortical culture, short-term treatment (15 min) with Hal-Flu combination and Clz increased GABAAβ subunit phosphorylation levels. Pretreatment of the cells with PKC inhibitor abolished the effect of the combined treatment, or Clz on phosphorylation of GABA(A) receptor. Inhibition of ERK2 did not alter the effect of drugs on GABA(A) receptor phosphorylation levels. Our findings provide evidence that the combined treatment regulates GABA(A) receptor function and does so via a PKC-dependent pathway.

Signaling pathways mediating phosphorylation and inactivation of glycogen synthase kinase-3β by the recombinant human δ-opioid receptor stably expressed in Chinese hamster ovary cells

Besides being involved in analgesia, δ-opioid receptors have recently been shown to exert antidepressant-like and neuroprotective effects. Glycogen synthase kinase-3β (GSK-3β), a key enzyme involved in cellular apoptosis and in mood disorders, may constitute a molecular target of δ-opioid receptors. However, relatively little is known on how δ-opioid receptors affect the multiple signaling pathways regulating GSK-3β. In the present study, we show that activation of human δ-opioid receptors stably expressed in Chinese hamster ovary (CHO) cells induced a rapid GSK-3β phosphorylation on Ser9 and a significant inhibition of the kinase activity. This effect was dependent on G proteins Gi/Go, unaffected by cell transfection with the Gβγ scavenger transducin, required the Src non-receptor tyrosine kinase and the specific involvement of the α isoform of phosphatidylinositol 3-kinase. δ-Opioid agonists activated the protein kinase Akt in a Src-dependent manner and chemical inhibition of Akt or stable expression of a dominant negative Akt1 mutant reduced the stimulation of GSK-3β phosphorylation. Moreover, δ-opioid receptor regulation of Akt and GSK-3β was dependent on transphosphorylation and transactivation of platelet-derived growth factor and insulin-like growth factor-1 receptor tyrosine kinases. AMP-activated protein kinase (AMPK) activity was also required, as δ-opioid effects on Akt and GSK-3β were mimicked by the AMPK activator A-769662 and reduced by the AMPK inhibitor Compound C. Conversely, inhibition of protein kinase C isoforms, extracellular signal-regulated protein kinases 1/2 and mammalian target of rapamycin was without effect, although the latter two kinases were activated by δ-opioid agonists. The results identify Src-dependent transactivation of receptor tyrosine kinases as a key process in δ-opioid receptor inhibitory control of GSK-3β and reveal a novel δ-opioid regulatory mechanism mediated by AMPK. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Glycogen synthase kinase 3: a point of convergence for the host inflammatory response

The phosphatidylinositol 3-kinase (PI3K) pathway has been shown to play a central role in regulating the host inflammatory response. Recent studies characterizing the downstream effector molecules within the PI3K pathway have identified that the serine/threonine kinase, glycogen synthase kinase 3 (GSK3), plays a pivotal role in regulating the production of pro- and anti-inflammatory cytokines. In innate immune cells, GSK3 inactivation augments anti-inflammatory cytokine production while concurrently suppressing the production of pro-inflammatory cytokines. The role of GSK3 in T cell biology has also been studied in detail and is involved in regulating multiple downstream signaling processes mediated by the T cell receptor (TCR), the co-stimulatory molecule CD28, and the IL-17 receptor. In vivo studies assessing the therapeutic properties of GSK3 inhibitors have shown that the inactivation of GSK3 can protect the host from immune-mediated pathology and death. This review will highlight the immunological importance GSK3 plays within different signal transduction pathways of the immune system, the cellular mechanisms regulating the activity of GSK3, the role of GSK3 in innate and adaptive immune responses, and the in vivo use of GSK3 inhibitors to treat inflammatory mediated diseases in animals.

Molecular pharmacology in a simple model system: implicating MAP kinase and phosphoinositide signalling in bipolar disorder

Understanding the mechanisms of drug action has been the primary focus for pharmacological researchers, traditionally using rodent models. However, non-sentient model systems are now increasingly being used as an alternative approach to better understand drug action or targets. One of these model systems, the social amoeba Dictyostelium, enables the rapid ablation or over-expression of genes, and the subsequent use of isogenic cell culture for the analysis of cell signalling pathways in pharmacological research. The model also supports an increasingly important ethical view of research, involving the reduction, replacement and refinement of animals in biomedical research. This review outlines the use of Dictyostelium in understanding the pharmacological action of two commonly used bipolar disorder treatments (valproic acid and lithium). Both of these compounds regulate mitogen activated protein (MAP) kinase and inositol phospholipid-based signalling by unknown means. Analysis of the molecular pathways targeted by these drugs in Dictyostelium and translation of discoveries to animal systems has helped to further understand the molecular mechanisms of these bipolar disorder treatments.

Molecular actions and therapeutic potential of lithium in preclinical and clinical studies of CNS disorders

Lithium has been used clinically to treat bipolar disorder for over half a century, and remains a fundamental pharmacological therapy for patients with this illness. Although lithium's therapeutic mechanisms are not fully understood, substantial in vitro and in vivo evidence suggests that it has neuroprotective/neurotrophic properties against various insults, and considerable clinical potential for the treatment of several neurodegenerative conditions. Evidence from pharmacological and gene manipulation studies support the notion that glycogen synthase kinase-3 inhibition and induction of brain-derived neurotrophic factor-mediated signaling are lithium's main mechanisms of action, leading to enhanced cell survival pathways and alteration of a wide variety of downstream effectors. By inhibiting N-methyl-D-aspartate receptor-mediated calcium influx, lithium also contributes to calcium homeostasis and suppresses calcium-dependent activation of pro-apoptotic signaling pathways. In addition, lithium decreases inositol 1,4,5-trisphosphate by inhibiting phosphoinositol phosphatases, a process recently identified as a novel mechanism for inducing autophagy. Through these mechanisms, therapeutic doses of lithium have been demonstrated to defend neuronal cells against diverse forms of death insults and to improve behavioral as well as cognitive deficits in various animal models of neurodegenerative diseases, including stroke, amyotrophic lateral sclerosis, fragile X syndrome, as well as Huntington's, Alzheimer's, and Parkinson's diseases, among others. Several clinical trials are also underway to assess the therapeutic effects of lithium for treating these disorders. This article reviews the most recent findings regarding the potential targets involved in lithium's neuroprotective effects, and the implication of these findings for the treatment of a variety of diseases.

Therapeutic Strategies to Increase Human β-Cell Growth and Proliferation by Regulating mTOR and GSK-3/β-Catenin Pathways

This perspective delineates approaches to develop therapeutic strategies to stimulate the proliferative potential of adult human β-cells in vitro. Previous findings demonstrated that nutrients, through regulation of mTOR signaling, promote regenerative processes including DNA synthesis, cell cycle progression and β-cell proliferation in rodent islets but rarely in human islets. Recently, we discovered that regulation of the Wnt/GSK-3/β-catenin pathway by directly inhibiting GSK-3 with pharmacologic agents, in combination with nutrient activation of mTOR, was required to increase growth and proliferation in human islets. Studies also revealed that nuclear translocation of β-catenin in response to GSK-3 inhibition regulated these processes and was rapamycin sensitive, indicating a role for mTOR. Human islets displayed a high level of insulin resistance consistent with the inability of exogenous insulin to activate Akt and engage the Wnt pathway by GSK-3 inhibition. This insulin resistance in human islets is not present in rodent islets and may explain the differential requirement in human islets to inhibit GSK-3 to enhance these regenerative processes. Human islets exhibited normal insulin secretion but a loss of insulin content, which was independent of all treatment conditions. The loss of insulin content may be related to insulin resistance, the isolation process or culture conditions. In this perspective, we provide strategies to enhance the proliferative capacity of adult human β-cells and highlight important differences between human and rodent islets: the lack of a nutrient response, requirement for direct GSK-3 inhibition, insulin resistance and loss of insulin content that emphasize the physiological significance of conducting studies in human islets.

Association study of the GSK-3B gene with tardive dyskinesia in European Caucasians

There is solid evidence of a genetic predisposition to tardive dyskinesia (TD) although the pathophysiological mechanisms of TD are still unclear. Nevertheless, the dopamine overactivity hypothesis of the TD etiology receives support from both pharmacological and physiological evidence. Dopaminergic signaling modulates the glycogen synthase kinase 3B (GSK-3B), a kinase that may play a critical role in the pathogenesis of neurodegenerative diseases. GSK-3B is an essential element of the apoptotic signaling cascade induced by oxidative stress, which may be involved in TD pathogenesis. We investigated whether GSK-3B polymorphisms (rs11919783, rs6805251, rs7624540, rs6438552, rs4072520, rs9878473, rs6779828 and rs3755557) selected using tagging method were associated with TD manifestation and abnormal involuntary movement severity. We evaluated 215 schizophrenia subjects from whom 169 were European Caucasians. All eight evaluated variants had their minor allele carriers consistently showing lower risk to TD and lower Abnormal Involuntary Movement Scale. The rs6805251, rs6438552 and rs9878473 variants showed a trend for association with TD in European Caucasian subjects (permuted p=0.07). Furthermore, all tested markers showed p< or =0.0007 after we incorporated age as covariate in the analysis of the abnormal involuntary movement severity. Our results suggest that GSK-3B polymorphism may play a role in the genetic vulnerability to TD manifestation in schizophrenia subjects with European Caucasian background further implicating polymorphisms in the dopamine D2-like receptor signaling in this context. These findings should be read with caution particularly before independent replication.

Wnt2 expression and signaling is increased by different classes of antidepressant treatments

BACKGROUND

Despite recent interest in glycogen synthase kinase-3beta (GSK-3beta) as a target for the treatment of mood disorders, there has been very little work related to these illnesses on the upstream signaling molecules that regulate this kinase as well as downstream targets.

METHODS

With a focused microarray approach we examined the influence of different classes of antidepressants on Wnt signaling that controls GSK-3beta activity as well as the transcription factors that contribute to the actions of GSK-3beta.

RESULTS

The results demonstrate that Wnt2 is a common target of different classes of antidepressants and also show differential regulation of Wnt-GSK-3beta signaling genes. Increased expression and function of Wnt2 was confirmed by secondary measures. Moreover, with a viral vector approach we demonstrate that increased expression of Wnt2 in the hippocampus is sufficient to produce antidepressant-like behavioral actions in well-established models of depression and treatment response.

CONCLUSIONS

These findings demonstrate that Wnt2 expression and signaling is a common target of antidepressants and that increased Wnt2 is sufficient to produce antidepressant effects.

GSK-3β activity and hyperdopamine-dependent behaviors

Dopamine plays important roles in normal brain function and many neuropsychiatric disorders. Classically, dopamine receptors are positively coupled to G protein-mediated signaling to regulate cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-dopamine and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) and Ca(2+) pathways. However, emerging evidence indicates that under hyperdopaminergic conditions, the protein kinase B (Akt)-glycogen synthase kinase 3β (GSK-3β) signaling cascade may mediate dopamine actions via D(2)-like receptors. This cAMP-independent signaling pathway involves the regulation of downstream synaptic targets, e.g., AMPA receptor, NMDA receptors, and thus synaptic plasticity. Here we provide an overview of how this novel signaling pathway relays dopamine receptor-mediated responses, particularly hyperdopamine-dependent behaviors. We discuss the relevance of the Akt/GSK-3β signaling cascade for the expression of dopamine-dependent behaviors and the drug actions associated with dopaminergic systems.

The antinociceptive effects of AR-A014418, a selective inhibitor of glycogen synthase kinase-3 beta, in mice

We investigated the antinociceptive effects of AR-A014418, a selective inhibitor of glycogen synthase kinase-3β (GSK-3β) in mice. A 30-minute pretreatment with AR-A014418 (.1 and 1 mg/kg, intraperitoneal [ip]) inhibited nociception induced by an ip injection of acetic acid. AR-A014418 pretreatment (.1 and .3 mg/kg, ip) also decreased the late (inflammatory) phase of formalin-induced licking, without affecting responses of the first (neurogenic) phase. In a different set of experiments, AR-A014418 (.1-10 μg/site) coinjected intraplantarly (ipl) with formalin inhibited the late phase of formalin-induced nociception. Furthermore, AR-A014418 administration (1 and 10 ng/site, intrathecal [it]) inhibited both phases of formalin-induced licking. In addition, AR-A014418 coinjection (10 ng/site, it) inhibited nociception induced by glutamate, N-methyl-D-aspartate (NMDA), (±)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD), tumor necrosis factor-alpha (TNF-α), and interleukin-1beta (IL-1β) by 47 ± 12%, 48 ± 11%, 31 ± 8%, 46 ± 13%, and 44 ± 11%, respectively. In addition, a 30-minute pretreatment with NP031115 (3 and 10 mg/kg, ip), a different GSK-3 β inhibitor, also attenuated the late phase of formalin-induced nociception. Collectively, these results provide convincing evidence that AR-A014418, given by local, systemic, and central routes, produces antinociception in several mouse models of nociception. The AR-A014418-dependent antinociceptive effects were induced by modulation of the glutamatergic system through metabotropic and ionotropic (NMDA) receptors and the inhibition of the cytokine (TNF-α and IL-1β) signaling.

PERSPECTIVE

These results suggest that GSK-3β may be a novel pharmacological target for the treatment of pain.

Dixdc1 is a critical regulator of DISC1 and embryonic cortical development

The psychiatric illness risk gene Disrupted in Schizophrenia-1 (DISC1) plays an important role in brain development; however, it is unclear how DISC1 is regulated during cortical development. Here, we report that DISC1 is regulated during embryonic neural progenitor proliferation and neuronal migration through an interaction with DIX domain containing-1 (Dixdc1), the third mammalian gene discovered to contain a Disheveled-Axin (DIX) domain. We determined that Dixdc1 functionally interacts with DISC1 to regulate neural progenitor proliferation by co-modulating Wnt-GSK3beta/beta-catenin signaling. However, DISC1 and Dixdc1 do not regulate migration via this pathway. During neuronal migration, we discovered that phosphorylation of Dixdc1 by cyclin-dependent kinase 5 (Cdk5) facilitates its interaction with the DISC1-binding partner Ndel1. Furthermore, Dixdc1 phosphorylation and its interaction with DISC1/Ndel1 in vivo is required for neuronal migration. Together, these data reveal that Dixdc1 integrates DISC1 into Wnt-GSK3beta/beta-catenin-dependent and -independent signaling pathways during cortical development and further delineate how DISC1 contributes to neuropsychiatric disorders.

Pharmacological and genetic reversal of age-dependent cognitive deficits attributable to decreased presenilin function

Alzheimer's disease (AD) is the leading cause of cognitive loss and neurodegeneration in the developed world. Although its genetic and environmental causes are not generally known, familial forms of the disease (FAD) are attributable to mutations in a single copy of the Presenilin (PS) and amyloid precursor protein genes. The dominant inheritance pattern of FAD indicates that it may be attributable to gain or change of function mutations. Studies of FAD-linked forms of presenilin (psn) in model organisms, however, indicate that they are loss of function, leading to the possibility that a reduction in PS activity might contribute to FAD and that proper psn levels are important for maintaining normal cognition throughout life. To explore this issue further, we have tested the effect of reducing psn activity during aging in Drosophila melanogaster males. We have found that flies in which the dosage of psn function is reduced by 50% display age-onset impairments in learning and memory. Treatment with metabotropic glutamate receptor (mGluR) antagonists or lithium during the aging process prevented the onset of these deficits, and treatment of aged flies reversed the age-dependent deficits. Genetic reduction of Drosophila metabotropic glutamate receptor (DmGluRA), the inositol trisphosphate receptor (InsP(3)R), or inositol polyphosphate 1-phosphatase also prevented these age-onset cognitive deficits. These findings suggest that reduced psn activity may contribute to the age-onset cognitive loss observed with FAD. They also indicate that enhanced mGluR signaling and calcium release regulated by InsP(3)R as underlying causes of the age-dependent cognitive phenotypes observed when psn activity is reduced.

From the cell to the clinic: a comparative review of the partial D₂/D₃receptor agonist and α2-adrenoceptor antagonist, piribedil, in the treatment of Parkinson's disease

Though L-3,4-dihydroxyphenylalanine (L-DOPA) is universally employed for alleviation of motor dysfunction in Parkinson's disease (PD), it is poorly-effective against co-morbid symptoms like cognitive impairment and depression. Further, it elicits dyskinesia, its pharmacokinetics are highly variable, and efficacy wanes upon long-term administration. Accordingly, "dopaminergic agonists" are increasingly employed both as adjuncts to L-DOPA and as monotherapy. While all recognize dopamine D(2) receptors, they display contrasting patterns of interaction with other classes of monoaminergic receptor. For example, pramipexole and ropinirole are high efficacy agonists at D(2) and D(3) receptors, while pergolide recognizes D(1), D(2) and D(3) receptors and a broad suite of serotonergic receptors. Interestingly, several antiparkinson drugs display modest efficacy at D(2) receptors. Of these, piribedil displays the unique cellular signature of: 1), signal-specific partial agonist actions at dopamine D(2)and D(3) receptors; 2), antagonist properties at α(2)-adrenoceptors and 3), minimal interaction with serotonergic receptors. Dopamine-deprived striatal D(2) receptors are supersensitive in PD, so partial agonism is sufficient for relief of motor dysfunction while limiting undesirable effects due to "over-dosage" of "normosensitive" D(2) receptors elsewhere. Further, α(2)-adrenoceptor antagonism reinforces adrenergic, dopaminergic and cholinergic transmission to favourably influence motor function, cognition, mood and the integrity of dopaminergic neurones. In reviewing the above issues, the present paper focuses on the distinctive cellular, preclinical and therapeutic profile of piribedil, comparisons to pramipexole, ropinirole and pergolide, and the core triad of symptoms that characterises PD-motor dysfunction, depressed mood and cognitive impairment. The article concludes by highlighting perspectives for clarifying the mechanisms of action of piribedil and other antiparkinson agents, and for optimizing their clinical exploitation.

Novel insights into lithium's mechanism of action: neurotrophic and neuroprotective effects

The monovalent cation lithium partially exerts its effects by activating neurotrophic and neuroprotective cellular cascades. Here, we discuss the effects of lithium on oxidative stress, programmed cell death (apoptosis), inflammation, glial dysfunction, neurotrophic factor functioning, excitotoxicity, and mitochondrial stability. In particular, we review evidence demonstrating the action of lithium on cyclic adenosine monophosphate (cAMP)-mediated signal transduction, cAMP response element binding activation, increased expression of brain-derived neurotrophic factor, the phosphatidylinositide cascade, protein kinase C inhibition, glycogen synthase kinase 3 inhibition, and B-cell lymphoma 2 expression. Notably, we also review data from clinical studies demonstrating neurotrophic effects of lithium. We expect that a better understanding of the clinically relevant pathophysiological targets of lithium will lead to improved treatments for those who suffer from mood as well as neurodegenerative disorders.

Does subtle disturbance of neuronal migration contribute to schizophrenia and other neurodevelopmental disorders? Potential genetic mechanisms with possible treatment implications

Pathways associated with genes that regulate neuronal migration by influencing the function of microtubules in the developing fetal brain may be interfered with as part of the "first-hit" of schizophrenia. In the fully-developed brain, these same pathways that impact microtubule function mediate at least some aspects of experience-dependent plasticity, which may also be impaired in schizophrenia. Whereas severe presentations of "lissencephaly" are associated with mutations and deletions of DISC1, LIS1 and the gene for the very low-density lipoprotein receptor, genetic variations of these loci are good candidate schizophrenia genes. Importantly, in the fully-developed brain, there is a possibility that at least some of the consequences of these disturbed genetic pathways that adversely affect microtubule function may be "bypassed" or mitigated.

GSK3beta: role in therapeutic landscape and development of modulators

Glycogen synthase kinase-3 beta (GSK3beta) is a multifunctional serine/threonine kinase which was originally identified as a regulator of glycogen metabolism. It plays a key role in the regulation of numerous signalling pathways including cellular process such as cell cycle, inflammation and cell proliferation. Over the last few years there is a considerable rise in the number of journals and patents publication by different workers worldwide. Many pharmaceutical companies are focusing on GSK3beta as a therapeutic target for the treatment of disease conditions. The present review is focused on signalling pathways of different disease conditions where GSK3beta is implicated. In this review, we present a comprehensive map of GSK3beta signalling pathways in disease physiologies. Structural analysis of GSK3beta along with molecular modelling reports from numerous workers are reviewed in context of design and development of GSK3beta inhibitors. Patent landscape of the small molecule modulators is profiled. The chemo space for small molecule modulators extracted from public and proprietary Kinase Chembiobase for GSK3beta are discussed. Compounds in different clinical phases of discovery are analysed. The review ends with the overall status of this important therapeutic target and challenges in development of its modulators.

Population-based linkage analysis of schizophrenia and bipolar case-control cohorts identifies a potential susceptibility locus on 19q13

Population-based linkage analysis is a new method for analysing genomewide single nucleotide polymorphism (SNP) genotype data in case-control samples, which does not assume a common disease, common variant model. The genome is scanned for extended segments that show increased identity-by-descent sharing within case-case pairs, relative to case-control or control-control pairs. The method is robust to allelic heterogeneity and is suited to mapping genes which contain multiple, rare susceptibility variants of relatively high penetrance. We analysed genomewide SNP datasets for two schizophrenia case-control cohorts, collected in Aberdeen (461 cases, 459 controls) and Munich (429 cases, 428 controls). Population-based linkage testing must be performed within homogeneous samples and it was therefore necessary to analyse the cohorts separately. Each cohort was first subjected to several procedures to improve genetic homogeneity, including identity-by-state outlier detection and multidimensional scaling analysis. When testing only cases who reported a positive family history of major psychiatric disease, consistent with a model of strongly penetrant susceptibility alleles, we saw a distinct peak on chromosome 19q in both cohorts that appeared in meta-analysis (P=0.000016) to surpass the traditional level for genomewide significance for complex trait linkage. The linkage signal was also present in a third case-control sample for familial bipolar disorder, such that meta-analysing all three datasets together yielded a linkage P=0.0000026. A model of rare but highly penetrant disease alleles may be more applicable to some instances of major psychiatric diseases than the common disease common variant model, and we therefore suggest that other genome scan datasets are analysed with this new, complementary method.

Light and electron microscopy study of glycogen synthase kinase-3beta in the mouse brain

Glycogen synthase kinase-3β (GSK3β) is highly abundant in the brain. Various biochemical analyses have indicated that GSK3β is localized to different intracellular compartments within brain cells. However, ultrastructural visualization of this kinase in various brain regions and in different brain cell types has not been reported. The goal of the present study was to examine GSK3β distribution and subcellular localization in the brain using immunohistochemistry combined with light and electron microscopy. Initial examination by light microscopy revealed that GSK3β is expressed in brain neurons and their dendrites throughout all the rostrocaudal extent of the adult mouse brain, and abundant GSK3β staining was found in the cortex, hippocampus, basal ganglia, the cerebellum, and some brainstem nuclei. Examination by transmission electron microscopy revealed highly specific subcellular localization of GSK3β in neurons and astrocytes. At the subcellular level, GSK3β was present in the rough endoplasmic reticulum, free ribosomes, and mitochondria of neurons and astrocytes. In addition GSK3β was also present in dendrites and dendritic spines, with some postsynaptic densities clearly labeled for GSK3β. Phosphorylation at serine-9 of GSK3β (pSer9GSK3β) reduces kinase activity. pSer9GSK3β labeling was present in all brain regions, but the pattern of staining was clearly different, with an abundance of labeling in microglia cells in all regions analyzed and much less neuronal staining in the subcortical regions. At the subcellular level pSer9GSK3β labeling was located in the endoplasmic reticulum, free ribosomes and in some of the nuclei. Overall, in normal brains constitutively active GSK3β is predominantly present in neurons while pSer9GSK3β is more evident in resting microglia cells. This visual assessment of GSK3β localization within the subcellular structures of various brain cells may help in understanding the diverse role of GSK3β signaling in the brain.

Lithium ameliorates altered glycogen synthase kinase-3 and behavior in a mouse model of fragile X syndrome

Fragile X syndrome (FXS), the most common form of inherited mental retardation and a genetic cause of autism, results from mutated fragile X mental retardation-1 (Fmr1). This study examined the effects on glycogen synthase kinase-3 (GSK3) of treatment with a metabotropic glutamate receptor (mGluR) antagonist, MPEP, and the GSK3 inhibitor, lithium, in C57Bl/6 Fmr1 knockout mice. Increased mGluR signaling may contribute to the pathology of FXS, and the mGluR5 antagonist MPEP increased inhibitory serine-phosphorylation of brain GSK3 selectively in Fmr1 knockout mice but not in wild-type mice. Inhibitory serine-phosphorylation of GSK3 was lower in Fmr1 knockout, than wild-type, mouse brain regions and was increased by acute or chronic lithium treatment, which also increased hippocampal brain-derived neurotrophic factor levels. Fmr1 knockout mice displayed alterations in open-field activity, elevated plus-maze, and passive avoidance, and these differences were ameliorated by chronic lithium treatment. These findings support the hypothesis that impaired inhibition of GSK3 contributes to the pathogenesis of FXS and support GSK3 as a potential therapeutic target.