Is glycogen synthase kinase-3 a central modulator in mood regulation?

Neuroglialpharmacology: myelination as a shared mechanism of action of psychotropic treatments

Current psychiatric diagnostic schema segregate symptom clusters into discrete entities, however, large proportions of patients suffer from comorbid conditions that fit neither diagnostic nor therapeutic schema. Similarly, psychotropic treatments ranging from lithium and antipsychotics to serotonin reuptake inhibitors (SSRIs) and acetylcholinesterase inhibitors have been shown to be efficacious in a wide spectrum of psychiatric disorders ranging from autism, schizophrenia (SZ), depression, and bipolar disorder (BD) to Alzheimer's disease (AD). This apparent lack of specificity suggests that psychiatric symptoms as well as treatments may share aspects of pathophysiology and mechanisms of action that defy current symptom-based diagnostic and neuron-based therapeutic schema. A myelin-centered model of human brain function can help integrate these incongruities and provide novel insights into disease etiologies and treatment mechanisms. Available data are integrated herein to suggest that widely used psychotropic treatments ranging from antipsychotics and antidepressants to lithium and electroconvulsive therapy share complex signaling pathways such as Akt and glycogen synthase kinase-3 (GSK3) that affect myelination, its plasticity, and repair. These signaling pathways respond to neurotransmitters, neurotrophins, hormones, and nutrition, underlie intricate neuroglial communications, and may substantially contribute to the mechanisms of action and wide spectra of efficacy of current therapeutics by promoting myelination. Imaging and genetic technologies make it possible to safely and non-invasively test these hypotheses directly in humans and can help guide clinical trial efforts designed to correct myelination abnormalities. Such efforts may provide insights into novel avenues for treatment and prevention of some of the most prevalent and devastating human diseases.

Desipramine selectively potentiates norepinephrine-elicited ERK1/2 activation through the α2A adrenergic receptor

The precise physiological effects of antidepressant drugs, and in particular their actions at non-monoamine transporter targets, are largely unknown. We have recently identified the tricyclic antidepressant drug desipramine (DMI) as a direct ligand at the α(2A) adrenergic receptor (AR) without itself driving heterotrimeric G protein/downstream effector activation [5]. In this study, we report our novel finding that DMI modulates α(2A)AR signaling in response to the endogenous agonist norepinephrine (NE). DMI acted as a signaling potentiator, selectively enhancing NE-induced α(2A)AR-mediated ERK1/2 MAPK signaling. This potentiation of ERK1/2 activation was observed as an increase in NE response sensitivity and a prolongation of the activation kinetics. DMI in a physiologically relevant ratio with NE effectively turned on ERK1/2 signaling that is lacking in response to physiological NE alone. Further, the DMI-induced ERK1/2 potentiation relied on heterotrimeric G(i/o) proteins and was arrestin-independent. This modulatory effect of DMI on NE signaling provides novel insight into the effects of this antidepressant drug on the noradrenergic system which it regulates, insight which enhances our understanding of the therapeutic mechanism for DMI.

Csnk1e is a genetic regulator of sensitivity to psychostimulants and opioids

Csnk1e, the gene encoding casein kinase 1-epsilon, has been implicated in sensitivity to amphetamines. Additionally, a polymorphism in CSNK1E was associated with heroin addiction, suggesting that this gene may also affect opioid sensitivity. In this study, we first conducted genome-wide quantitative trait locus (QTL) mapping of methamphetamine (MA)-induced locomotor activity in C57BL/6J (B6) × DBA/2J (D2)-F(2) mice and a more highly recombinant F(8) advanced intercross line. We identified a QTL on chromosome 15 that contained Csnk1e (63-86 Mb; Csnk1e=79.25 Mb). We replicated this result and further narrowed the locus using B6.D2(Csnk1e) and D2.B6(Csnk1e) reciprocal congenic lines (78-86.8 and 78.7-81.6 Mb, respectively). This locus also affected sensitivity to the μ-opioid receptor agonist fentanyl. Next, we directly tested the hypothesis that Csnk1e is a genetic regulator of sensitivity to psychostimulants and opioids. Mice harboring a null allele of Csnk1e showed an increase in locomotor activity following MA administration. Consistent with this result, coadministration of a selective pharmacological inhibitor of Csnk1e (PF-4800567) increased the locomotor stimulant response to both MA and fentanyl. These results show that a narrow genetic locus that contains Csnk1e is associated with differences in sensitivity to MA and fentanyl. Furthermore, gene knockout and selective pharmacological inhibition of Csnk1e define its role as a negative regulator of sensitivity to psychostimulants and opioids.

Noradrenergic antidepressant responses to desipramine in vivo are reciprocally regulated by arrestin3 and spinophilin

Many antidepressant drugs, including the tricyclic antidepressant desipramine (DMI), are broadly understood to function by modulating central noradrenergic neurotransmission. α(2) adrenergic receptors (α(2)ARs) are key regulators of the noradrenergic system, and previous work has implicated α(2)ARs in mediating the antidepressant activity of DMI in the rodent forced swim test (FST). However, little is known about intracellular regulators of antidepressant drug action. α(2)AR function is tightly regulated by its intracellular interacting partners arrestin and the dendritic protein spinophilin. We have previously established the competitive and reciprocal nature of these interacting proteins at the α(2)AR in the context of classic agonist effects, and have shown DMI to be a direct arrestin-biased ligand at the receptor. In the present study, we report that mice deficient in the α(2A)AR subtype lack DMI-induced antidepressant behavioral effects in the FST. As well, mice deficient in arrestin3 lack antidepressant response to DMI, while spinophilin-null mice have enhanced antidepressant response to DMI compared with wild-type controls, indicating that this α(2A)AR-mediated response is reciprocally regulated by arrestin and spinophilin. The characteristic of α(2A)AR-dependence and arrestin3 involvement was shared by the antidepressant effect of the classic α(2)AR agonist clonidine but not the non-tricyclic norepinephrine reuptake inhibitor reboxetine, supporting a model whereby DMI exerts its antidepressant effect through direct engagement of the α(2A)AR and arrestin3. Our results implicate arrestin- and spinophilin-mediated regulation of the α(2A)AR in the pharmacology of the noradrenergic antidepressant DMI, and suggest that manipulation of this mode of receptor regulation may represent a novel and viable therapeutic strategy.

Gene-gene interaction of glycogen synthase kinase 3-β and serotonin transporter on human antidepressant response to sleep deprivation

BACKGROUND

Glycogen synthase kinase 3-β (GSK3-β) is involved in the control of cell behavior and in the mechanism of action of lithium and serotonergic antidepressants, and in humans a promoter variant (rs334558*C) was associated with reduced activity and better antidepressant response. The short form of a polymorphism in the promoter in the serotonin transporter (5-HTTLPR) has been consistently associated with worse antidepressant response. In animals the knockout of GSK3-β counteracts the depressive-like behavioral effects of 5-HT inhibition.

METHODS

With a translational approach, we studied the effect of 5-HTTLPR and rs334558 on antidepressant response to sleep deprivation in a unique sample of 122 patients affected by a major depressive episode in course of bipolar disorder. Mood was self rated on Visual Analog Scales, and severity of depression was rated on Montgomery-Asberg rating scale.

RESULTS

We observed a triple interaction of 5-HTTLPR, rs334558 and treatment on severity of depression. While among rs334558 T/T homozygotes the best antidepressant response was associated with 5-HTTLPR l/l homozygosity, among the rs334558 C carriers the 5-HTTLPR s/s showed the best response to treatment.

CONCLUSIONS

A gene promoter polymorphism which reduces the activity of GSK3-β counteracts the detrimental influence of the short form of the 5-HT promoter on antidepressant response. A key component of Wnt pathway, and upstream of the mTOR signaling cascade, GSK3-β influences synaptic plasticity and cell resilience. Gene-gene interactions between components of the monoaminergic signal transduction pathways and of plasticity related pathways can shape the individual antidepressant response.

GSK-3 and Wnt Signaling in Neurogenesis and Bipolar Disorder

The canonical Wnt signaling pathway is critical for development of the mammalian central nervous system and regulates diverse processes throughout adulthood, including adult neurogenesis. Glycogen synthase kinase-3 (GSK-3) antagonizes the canonical Wnt pathway and therefore also plays a central role in neural development and adult neurogenesis. Lithium, the first line of therapy for bipolar disorder, inhibits GSK-3, activates Wnt signaling and stimulates adult neurogenesis, which may be important for its therapeutic effects. GSK-3 also regulates other critical signaling pathways which may contribute to the therapeutic effects of lithium, including growth factor/neurotrophin signaling downstream of Akt. Here we will review the roles of GSK-3 in CNS development and adult neurogenesis, with a focus on the canonical Wnt pathway. We will also discuss the validation of GSK-3 as the relevant target of lithium and the mechanisms downstream of GSK-3 that influence mammalian behavior.

Signaling pathways underlying the pathophysiology and treatment of depression: novel mechanisms for rapid-acting agents

Basic and clinical studies demonstrate that stress and depression are associated with atrophy and loss of neurons and glia, which contribute to the decreased size and function of limbic brain regions that control mood and depression, including the prefrontal cortex and hippocampus. Here, we review findings that suggest that opposing effects of stress and/or depression and antidepressants on neurotrophic factor expression and signaling partly explain these effects. We also discuss recent reports that suggest a possible role for glycogen synthase kinase 3 and upstream wingless (Wnt)-frizzled (Fz) signaling pathways in mood disorders. New studies also demonstrate that the rapid antidepressant actions of NMDA receptor antagonists are associated with activation of glutamate transmission and induction of synaptogenesis, providing novel targets for a new generation of fast-acting, more efficacious therapeutic agents.

Antipsychotics in the treatment of bipolar disorder

Atypical antipsychotics have an important role in the acute and maintenance treatment of bipolar disorder. While robust evidence supports the efficacy of these agents in the treatment of mania and in the prevention of manic relapse, few atypical antipsychotics have shown efficacy in the treatment or prevention of depressive episodes. These agents pose a lower risk of extrapyramidal side effects compared to typical neuroleptics, but carry a significant liability for weight gain and other metabolic side effects such as hyperglycemia and hyperlipidemia. More comparative effectiveness studies are needed to assess the optimal treatment regimens, including the relative benefits and risks of antipsychotics versus mood stabilizers. The exploration of the molecular mechanisms of antipsychotics has helped to shed further light on the underlying neurobiology of bipolar disorder, since these compounds target systems thought to be key to the pathophysiology of bipolar disorder. In addition to modulating monoaminergic neurotransmission, atypical antipsychotics appear to share properties with mood-stabilizing agents known to alter intracellular signal transduction leading to changes in neuronal activity and gene expression. Atypical antipsychotic drugs have been shown to exhibit neuroprotective properties that are mediated by upregulation of trophic and cellular resilience factors. Building on our understanding of existing therapeutics, especially as it relates to underlying disease pathology, newer "plasticity enhancing" strategies hold promise for future treatments of bipolar disorder.

Review of pharmacological treatment in mood disorders and future directions for drug development

After a series of serendipitous discoveries of pharmacological treatments for mania and depression several decades ago, relatively little progress has been made for novel hypothesis-driven drug development in mood disorders. Multifactorial etiologies of, and lack of a full understanding of, the core neurobiology of these conditions clearly have contributed to these development challenges. There are, however, relatively novel targets that have raised opportunities for progress in the field, such as glutamate and cholinergic receptor modulators, circadian regulators, and enzyme inhibitors, for alternative treatment. This review will discuss these promising new treatments in mood disorders, the underlying mechanisms of action, and critical issues of their clinical application. For these new treatments to be successful in clinical practice, it is also important to design innovative clinical trials that identify the specific actions of new drugs, and, ideally, to develop biomarkers for monitoring individualized treatment response. It is predicted that future drug development will identify new agents targeting the molecular mechanisms involved in the pathophysiology of mood disorders.

Fragile X syndrome: a psychiatric perspective

Fragile X syndrome (FXS) is associated with a complex but relatively consistent psychiatric phenotype. Recent research has suggested neural substrates for the behavioral abnormalities typically seen in FXS, and enhanced treatment strategies for managing disabling psychiatric comorbidity. While disease-specific, and possibly disease-modifying, therapeutics are being developed for FXS, currently available psychiatric medications can provide significant symptomatic relief of the hyperactivity, anxiety disorders, and affective disturbances often seen in the course of FXS. However, patients with fragile X may be especially susceptible to the psychiatric side effects of these medications, requiring particular care in prescribing. Recent findings concerning disease mechanisms and treatment strategies are reviewed from the perspective of a clinical psychiatrist, in an effort to enhance conventional pharmacotherapy of FXS.

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.

Signaling pathways underlying the rapid antidepressant actions of ketamine

Currently available medications have significant limitations, most notably low response rate and time lag for treatment response. Recent clinical studies have demonstrated that ketamine, an NMDA receptor antagonist produces a rapid antidepressant response (within hours) and is effective in treatment resistant depressed patients. Molecular and cellular studies in rodent models demonstrate that ketamine rapidly increases synaptogenesis, including increased density and function of spine synapses, in the prefrontal cortex (PFC). Ketamine also produces rapid antidepressant actions in behavioral models of depression, and reverses the deficits in synapse number and behavior resulting from chronic stress exposure. These effects of ketamine are accompanied by stimulation of the mammalian target of rapamycin (mTOR), and increased levels of synaptic proteins. Together these studies indicate that ketamine rapidly reverses the atrophy of spines in the PFC and thereby causes a functional reconnection of neurons that underlies the rapid behavioral responses. These findings identify new targets for rapid acting antidepressants that are safer than ketamine. This article is part of a Special Issue entitled 'Anxiety and Depression'.

A role for Akt and glycogen synthase kinase-3 as integrators of dopamine and serotonin neurotransmission in mental health

Mental illnesses, such as bipolar disorder, attention-deficit/hyperactivity disorder, depression and schizophrenia are a major public health concern worldwide. Several pharmacologic agents acting on monoamine neurotransmission are used for the management of these disorders. However, there is still little understanding of the ultimate molecular mechanisms responsible for the therapeutic effects of these drugs or their relations with disease etiology. Here I provide an overview of recent advances on the involvement of the signalling molecules Akt and glycogen synthase kinase-3 (GSK3) in the regulation of behaviour by the monoamine neurotransmitters dopamine (DA) and serotonin (5-HT). I examine the possible participation of these signalling molecules to the effects of antidepressants, lithium and antipsychotics, as well as their possible contribution to mental disorders. Regulation of Akt and GSK3 may constitute an important signalling hub in the subcellular integration of 5-HT and DA neurotransmission. It may also provide a link between the action of these neurotransmitters and gene products, like disrupted in schizophrenia 1 (DISC1) and neuregulin (NRG), that are associated with increased risk for mental disorders. However, changes in Akt and GSK3 signalling are not restricted to a single disorder, and their contribution to specific behavioural symptoms or therapeutic effects may be modulated by broader changes in biologic contexts or signalling landscapes. Understanding these interactions may provide a better understanding of mental illnesses, leading to better efficacy of new therapeutic approaches.

The roles of neurotrophic factor and Wnt signaling in depression

Depression is a debilitating disease with a lifetime prevalence of ~16% in the American population. In addition to the monoamine hypothesis, altered expressions of neurotrophic factors, growth factors, and Wnt signaling are implicated in the pathophysiology and treatment of depression. This review focuses on intracellular signaling cascades that underlie depression and treatment response.

Lithium ameliorates neurodegeneration, suppresses neuroinflammation, and improves behavioral performance in a mouse model of traumatic brain injury

Although traumatic brain injury (TBI) is recognized as one of the leading causes of death from trauma to the central nervous system (CNS), no known treatment effectively mitigates its effects. Lithium, a primary drug for the treatment of bipolar disorder, has been known to have neuroprotective effects in various neurodegenerative conditions such as stroke. Until this study, however, it has not been investigated as a post-insult treatment for TBI. To evaluate whether lithium could have beneficial effects following TBI, lithium at a dose of 1.5 mEq/kg was administered after injury. Assessed at 3 days and 3 weeks post-injury using hematoxylin and eosin staining, lithium treatment was found to reduce lesion volume. Lithium at doses of 2.0 and 3.0 mEq/kg also significantly reduced lesion volume at 3 days after injury, and the therapeutic window was at least 3 h post-injury. TBI-induced neuronal death, microglial activation, and cyclooxygenase-2 induction were all attenuated by lithium at 3 days after injury. In addition, lithium treatment reduced TBI-induced matrix metalloproteinase-9 expression and preserved the integrity of the blood-brain barrier. As for behavioral outcomes, lithium treatment reduced anxiety-like behavior in an open-field test, and improved short- and long-term motor coordination in rotarod and beam-walk tests. Lithium robustly increased serine phosphorylation of glycogen synthase kinase-3β (GSK-3β), suggesting that the underlying mechanisms responsible for lithium's protective effects are triggered by increasing phosphorylation of this kinase and thereby inhibiting its activity. Our results support the notion that lithium has heretofore unrecognized capacity to mitigate the neurodegenerative effects and improve functional outcomes in TBI.

Glycogen synthase kinase-3: a promising therapeutic target for fragile x syndrome

Recent advances in understanding the pathophysiological mechanisms contributing to fragile X syndrome (FXS) have increased optimism that drug interventions can provide significant therapeutic benefits. FXS results from inadequate expression of functional fragile X mental retardation protein (FMRP). FMRP may have several functions, but it is most well-established as an RNA binding protein that regulates translation, and it is thought that by this mechanism FMRP is capable of affecting numerous cellular processes by selectively regulating protein levels. The multiple cellular functions regulated by FMRP suggest that multiple interventions may be required for reversing the effects of deficient FMRP. Evidence that inhibitors of glycogen synthase kinase-3 (GSK3) may contribute to the therapeutic treatment of FXS is reviewed here. Lithium, a GSK3 inhibitor, improved function in the Drosophila model of FXS. In mice lacking FMRP expression (FX mice), GSK3 is hyperactive in several brain regions. Significant improvements in several FX-related phenotypes have been obtained in FX mice following the administration of lithium, and in some case other GSK3 inhibitors. These responses include normalization of heightened audiogenic seizure susceptibility and of hyperactive locomotor behavior, enhancement of passive avoidance learning retention and of sociability behaviors, and corrections of macroorchidism, neuronal spine density, and neural plasticity measured electrophysiologically as long term depression. A pilot clinical trial of lithium in patients with FXS also found improvements in several measures of behavior. Taken together, these findings indicate that lithium and other inhibitors of GSK3 are promising candidate therapeutic agents for treating FXS.

Glycogen Synthase Kinase-3 is an Intermediate Modulator of Serotonin Neurotransmission

Serotonin is a neurotransmitter with broad functions in brain development, neuronal activity, and behaviors; and serotonin is the prominent drug target in several major neuropsychiatric diseases. The multiple actions of serotonin are mediated by diverse serotonin receptor subtypes and associated signaling pathways. However, the key signaling components that mediate specific function of serotonin neurotransmission have not been fully identified. This review will provide evidence from biochemical, pharmacological, and animal behavioral studies showing that serotonin regulates the activation states of brain glycogen synthase kinase-3 (GSK3) via type 1 and type 2 serotonin receptors. In return, GSK3 directly interacts with serotonin receptors in a highly selective manner, with a prominent effect on modulating serotonin 1B receptor activity. Therefore, GSK3 acts as an intermediate modulator in the serotonin neurotransmission system, and balanced GSK3 activity is essential for serotonin-regulated brain function and behaviors. Particularly important, several classes of serotonin-modulating drugs, such as antidepressants and atypical antipsychotics, regulate GSK3 by inhibiting its activity in brain, which reinforces the importance of GSK3 as a potential therapeutic target in neuropsychiatric diseases associated with abnormal serotonin function.

Evidence for association of an ACCN1 gene variant with response to lithium treatment in Sardinian patients with bipolar disorder

AIMS

Bipolar disorder (BD) is a lifelong psychiatric illness characterized by manic and depressive episodes affecting 1-5% of the general population. Among mood-stabilizing treatments, lithium represents the mainstay in the therapeutic management of BD. However, besides the relatively high rate of excellent responders, a significant fraction of patients present patterns of partial or nonresponse to lithium. This variability might be influenced by genetic factors, even though findings have so far been inconclusive. Here, we present the results of an exploratory genome-wide scan followed by extended genotyping carried out on a sample of 204 Sardinian BD patients characterized for lithium response.

MATERIALS & METHODS

Phenotypic assessment of lithium response was made using the retrospective criteria of long-term treatment response scale. Using Affymetrix(®) 6.0 SNP arrays, we genotyped a subsample of 52 BD patients evenly distributed at the extreme ends of the treatment response scale. The associated SNPs were then prioritized and selected for validation and extended genotyping in the whole sample of BD patients characterized for lithium response. Association was also tested using the scale for a quantitative trait analysis.

RESULTS

Our findings showed that several SNPs were nominally associated (p ≤ 10(-5)) with lithium response in the subgroup of 52 BD subjects. Some association signals were then confirmed in the extended sample. The strongest association, also supported by the quantitative trait analysis, was shown for a SNP located in intron 1 of the ACCN1 gene, encoding for a cation channel with high affinity for sodium and permeable to lithium.

CONCLUSION

Our results indicate that ACCN1 gene is a potential candidate for response to lithium treatment that would serve as a genetic marker of lithium efficacy for BD patients.

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.

The psychiatric presentation of fragile x: evolution of the diagnosis and treatment of the psychiatric comorbidities of fragile X syndrome

Fragile X syndrome (FXS) is the leading inherited cause of mental retardation and autism spectrum disorders worldwide. It presents with a distinct behavioral phenotype which overlaps significantly with that of autism. Unlike autism and most common psychiatric disorders, the neurobiology of fragile X is relatively well understood. Lack of the fragile X mental retardation protein causes dysregulation of synaptically driven protein synthesis, which in turn causes global disruption of synaptic plasticity. Thus, FXS can be considered a disorder of synaptic plasticity, and a developmental disorder in the purest sense: mutation of the FMR1 (fragile X mental retardation 1) gene results in abnormal synaptic development in response to experience. Accumulation of this abnormal synaptic development, over time, leads to a characteristic and surprisingly consistent behavioral phenotype of attention deficit, hyperactivity, impulsivity, multiple anxiety symptoms, repetitive/perseverative/stereotypic behaviors, unstable affect, aggression, and self-injurious behavior. Many features of the behavioral and psychiatric phenotype of FXS follow a developmental course, waxing and waning over the life span. In most cases, symptoms present as a mixed clinical picture, not fitting established diagnostic categories. There have been many clinical trials in fragile X subjects, but no placebo-controlled trials of adequate size or methodology utilizing the most commonly prescribed psychiatric medications. However, large and well-designed trials of investigational agents which target the underlying pathology of FXS have recently been completed or are under way. While the literature offers little guidance to the clinician treating patients with FXS today, potentially disease-modifying treatments may be available in the near future.

Regulation by glycogen synthase kinase-3 of inflammation and T cells in CNS diseases

Elevated markers of neuroinflammation have been found to be associated with many psychiatric and neurodegenerative diseases, such as mood disorders, Alzheimer's disease, and multiple sclerosis (MS). Since neuroinflammation is thought to contribute to the pathophysiology of these diseases and to impair responses to therapeutic interventions and recovery, it is important to identify mechanisms that regulate neuroinflammation and potential targets for controlling neuroinflammation. Recent findings have demonstrated that glycogen synthase kinase-3 (GSK3) is an important regulator of both the innate and adaptive immune systems' contributions to inflammation. Studies of the innate immune system have shown that inhibitors of GSK3 profoundly alter the repertoire of cytokines that are produced both by peripheral and central cells, reducing pro-inflammatory cytokines, and increasing anti-inflammatory cytokines. Furthermore, inhibitors of GSK3 promote tolerance to inflammatory stimuli, reducing inflammatory cytokine production upon repeated exposure. Studies of the adaptive immune system have shown that GSK3 regulates the production of cytokines by T cells and the differentiation of T cells to subtypes, particularly Th17 cells. Regulation of transcription factors by GSK3 appears to play a prominent role in its regulation of immune responses, including of NF-κB, cyclic AMP response element binding protein, and signal transducer and activator of transcription-3. Invivo studies have shown that GSK3 inhibitors ameliorate clinical symptoms of both peripheral and central inflammatory diseases, particularly experimental autoimmune encephalomyelitis, the animal model of MS. Therefore, the development and application of GSK3 inhibitors may provide a new therapeutic strategy to reduce neuroinflammation associated with many central nervous system diseases.

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.

Transcriptomic profiles of Wnt3a and insulin in primary cultured rat cortical neurones

Glycogen synthase kinase 3 (GSK3) is a widely expressed, constitutively active, serine/threonine kinase that is negatively regulated by both Wnt and insulin via two independent signalling pathways. GSK3 is an important mediator in many physiological processes including glycogen metabolism, apoptosis and gene transcription. In addition, GSK3 is implicated in diseases such as Alzheimer's, schizophrenia and cancer, where it exhibits deregulated activity. In this study, we sought to determine the neuronal genes regulated by both Wnt and insulin in an in vitro cell culture model to further elucidate the signalling roles GSK3 plays in the CNS. Affymetrix Rat Genome 230 2.0 whole genome microarrays were used to explore the expression profiles of rat primary cortical neurones treated with recombinant Wnt3a (10 nM) or insulin (50 nM) for 2 h. Following a conservative correction (Bonferroni) for multiple testing, seven genes were identified to be differentially expressed from controls; four of these genes were regulated by insulin and three genes were regulated by both insulin and Wnt3a. The data were also analysed using a false discovery rate cut off, which is a less stringent correction for multiple testing. This approach yielded 105 genes that were differentially regulated from controls; 72 of the gene changes were attributable to insulin treatment, 11 were because of Wnt3a treatment and 22 genes were altered by both insulin and Wnt3a. These data demonstrate that the Wnt and insulin pathways exhibit both divergent and overlapping signalling activities in neuronal cells. The overlapping transcriptional response was not attributable to Wnt3a activating Akt. These findings have ramifications for neurodevelopment and neurological diseases, in which the Wnt and insulin signalling pathways are implicated.

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.

Proof of concept trials in bipolar disorder and major depressive disorder: a translational perspective in the search for improved treatments

A better understanding of the neurobiology of mood disorders, informed by preclinical research and bi-directionally translated to clinical research, is critical for the future development of new and effective treatments. Recently, diverse new targets/compounds have been specifically tested in preclinical models and in proof-of-concept studies, with potential relevance as treatments for mood disorders. Most of the evidence comes from case reports, case series, or controlled proof-of-concept studies, some with small sample sizes. These include (1) the opioid neuropeptide system, (2) the purinergic system, (3) the glutamatergic system, (4) the tachykinin neuropeptide system, (5) the cholinergic system (muscarinic system), and (6) intracellular signaling pathways. These targets may be of substantial interest in defining future directions in drug development, as well as in developing the next generation of therapeutic agents for the treatment of mood disorders. Overall, further study of these and similar drugs may lead to a better understanding of relevant and clinically useful drug targets in the treatment of these devastating illnesses.

Glycogen synthase kinase-3β is a functional modulator of serotonin-1B receptors

Glycogen synthase kinase-3 (GSK3) is a constitutively active protein kinase that is involved in neuronal regulation and is a potential pharmacological target of neurological disorders. We found previously that GSK3β selectively interacts with 5-hydroxytryptamine-1B receptors (5-HT1BR) that have important functions in serotonin neurotransmission and behavior. In this study, we provide new information supporting the importance of GSK3β in 5-HT1BR-regulated signaling, physiological function, and behaviors. Using molecular, biochemical, pharmacological, and behavioral approaches, we tested 5-HT1BR's interaction with G(i)α(2) and β-arrestin2 and 5-HT1BR-regulated signaling in cells, serotonin release in mouse cerebral cortical slices, and behaviors in wild-type and β-arrestin2 knockout mice. Molecular ablation of GSK3β and GSK3 inhibitors abolished serotonin-induced change of 5-HT1BR coupling to G(i)α(2) and associated signaling but had no effect on serotonin-induced recruitment of β-arrestin2 to 5-HT1BR. This effect is specific for 5-HT1BR because GSK3 inhibitors did not change the interaction between serotonin 1A receptors and G(i)α(2). Two GSK3 inhibitors, N-(4-methoxybenzyl)-N'-(5-nitro-1,3-thiazol-2-yl)urea (AR-A014418) and 3-(5-bromo-1-methyl-1H-indol-3-yl)-4-(benzofuran-3-yl)pyrrole-2,5-dione (BIP-135), efficiently abolished the inhibitory effect of the 5-HT1BR agonist anpirtoline on serotonin release in mouse cerebral cortical slices. GSK3 inhibitors also facilitated the 5-HT1BR agonist anpirtoline-induced behavioral effect in the tail suspension test but spared anpirtoline-induced locomotor activity. These results suggest that GSK3β is a functional selective modulator of 5-HT1BR-regulated signaling, and GSK3 inhibitors fine-tune the physiological and behavioral actions of 5-HT1BR. Future studies may elucidate the significant roles of GSK3 in serotonin neurotransmission and implications of GSK3 inhibitors as functional selective modulators of 5-HT1BR.

Regulation of glycogen synthase kinase-3 during bipolar mania treatment

OBJECTIVES

Bipolar disorder is a debilitating psychiatric illness presenting with recurrent mania and depression. The pathophysiology of bipolar disorder is poorly understood, and molecular targets in the treatment of bipolar disorder remain to be identified. Preclinical studies have suggested that glycogen synthase kinase-3 (GSK3) is a potential therapeutic target in bipolar disorder, but evidence of abnormal GSK3 in human bipolar disorder and its response to treatment is still lacking.

METHODS

This study was conducted in acutely ill type I bipolar disorder subjects who were hospitalized for a manic episode. The protein level and the inhibitory serine phosphorylation of GSK3 in peripheral blood mononuclear cells of bipolar manic and healthy control subjects were compared, and the response of GSK3 to antimanic treatment was evaluated.

RESULTS

The levels of GSK3α and GSK3β in this group of bipolar manic subjects were higher than healthy controls. Symptom improvement during an eight-week antimanic treatment with lithium, valproate, and atypical antipsychotics was accompanied by a significant increase in the inhibitory serine phosphorylation of GSK3, but not the total level of GSK3, whereas concomitant electroconvulsive therapy treatment during a manic episode appeared to dampen the response of GSK3 to pharmacological treatment.

CONCLUSIONS

Results of this study suggest that GSK3 can be modified during the treatment of bipolar mania. This finding in human bipolar disorder is in agreement with preclinical data suggesting that inhibition of GSK3 by increasing serine phosphorylation is a response of GSK3 to psychotropics used in bipolar disorder, supporting the notion that GSK3 is a promising molecular target in the pharmacological treatment of bipolar disorder.