A beta-arrestin 2 signaling complex mediates lithium action on behavior

Forebrain-specific deletion of Cdk5 in pyramidal neurons results in mania-like behavior and cognitive impairment

Cyclin-dependent kinase 5 (Cdk5) is associated with synaptic plasticity and cognitive function. Previous reports have demonstrated that Cdk5 is necessary for memory formation, although others have reported Cdk5 conditional knockout mouse models exhibiting enhanced learning and memory. Furthermore, how Cdk5 acts in specific cell populations to affect behavior and cognitive outcomes remains unclear. Here we conduct a behavioral characterization of a forebrain-specific Cdk5 conditional knockout mouse model under the αCaMKII promoter, in which Cdk5 is ablated in excitatory pyramidal neurons of the forebrain. The Cdk5 conditional knockouts exhibit hyperactivity in the open field, reduced anxiety, and reduced behavioral despair. Moreover, the Cdk5 conditional knockouts also display impaired spatial learning in the Morris water maze and are severely impaired in contextual fear memory, which correspond to deficits in synaptic transmission. Remarkably, the hyperactivity of the Cdk5 conditional knockouts can be ameliorated by the administration of lithium chloride, an inhibitor of GSK3β signaling. Collectively, our data reveal that Cdk5 ablation from forebrain excitatory neurons results in deleterious effects on emotional and cognitive behavior and highlight a key role for Cdk5 in regulating the GSK3β signaling pathway.

β-Arrestin-2 inhibits preference for alcohol in mice and suppresses Akt signaling in the dorsal striatum

In this study, we investigated the role of β-arrestin-2 in alcohol preference using the two-bottle choice and conditioned place preference procedures in wild-type (WT) and β-arrestin-2 knockout (KO) mice. Locomotion and righting reflex tests were performed to test alcohol sensitivity. The possible molecular signals regulated by β-arrestin-2 were analyzed by Western blot. We found that β-arrestin-2 KO mice showed a marked increase in voluntary alcohol consumption without significant differences in preference for saccharin or aversion to quinine. These animals also exhibited higher conditioned place preference scores for alcohol than WT mice. Meanwhile, KO mice showed reduced sensitivity to alcohol and increased blood alcohol clearance. Furthermore, after the free consumption of alcohol, the activities of protein kinase B and glycogen synthase kinase 3β (GSK3β) increased in the dorsal striatum of WT mice, but not in KO mice, which showed high basal activity of Akt in the dorsal striatum. These results suggest that β-arrestin-2 negatively regulates alcohol preference and reward, likely through regulating the activation of signaling pathways including Akt/GSK3β in the dorsal striatum.

Intracellular pathways of antipsychotic combined therapies: implication for psychiatric disorders treatment

Dysfunctions in the interplay among multiple neurotransmitter systems have been implicated in the wide range of behavioral, emotional and cognitive symptoms displayed by major psychiatric disorders, such as schizophrenia, bipolar disorder or major depression. The complex clinical presentation of these pathologies often needs the use of multiple pharmacological treatments, in particular (1) when monotherapy provides insufficient improvement of the core symptoms; (2) when there are concurrent additional symptoms requiring more than one class of medication and (3) in order to improve tolerability, by using two compounds below their individual dose thresholds to limit side effects. To date, the choice of drug combinations is based on empirical paradigm guided by clinical response. Nonetheless, several preclinical studies have demonstrated that drugs commonly used to treat psychiatric disorders may impact common intracellular target molecules (e.g. Akt/GSK-3 pathway, MAP kinases pathway, postsynaptic density proteins). These findings support the hypothesis that convergence at crucial steps of transductional pathways could be responsible for synergistic effects obtained in clinical practice by the co-administration of those apparently heterogeneous pharmacological compounds. Here we review the most recent evidence on the molecular crossroads in antipsychotic combined therapies with antidepressants, mood stabilizers, and benzodiazepines, as well as with antipsychotics. We first discuss clinical clues and efficacy of such combinations. Then we focus on the pharmacodynamics and on the intracellular pathways underpinning the synergistic, or concurrent, effects of each therapeutic add-on strategy, as well as we also critically appraise how pharmacological research may provide new insights on the putative molecular mechanisms underlying major psychiatric disorders.

Beta-arrestin2 is involved in the increase of distal colonic contraction in diabetic rats

Colonic dysmotility occurs in diabetes and the patients exhibit diarrhea or constipation. The pathogenetic mechanisms underlying colonic dysmotility in diabetic patients remain poorly understood. The effects of β-arrestin2 on colonic contraction in diabetic rats were investigated for the first time. Male SD rats were treated with a single intraperitoneally injected dose of streptozotocin, and those displaying sustained high blood glucose were selected as diabetes mellitus models. Longitudinal muscle strips of the distal colon were prepared to monitor contraction of the colon in vitro. Expression of β-arrestin2 was investigated by Western blot analysis. Anti-β-arrestin2 antibody had no direct effect on the contraction of distal colonic strips in both normal and diabetic rats. Carbachol-induced contractions of distal colonic strips were higher in diabetic rats than in normal rats. Anti-β-arrestin2 antibody partly blocked carbachol-induced increases of distal colonic strips in diabetic rats. The expression level of β-arrestin2 protein in the colon was higher in diabetic rats than in normal rats. These results suggest that β-arrestin2 is involved in the increase of distal colonic contraction in diabetic rats.

Characterization of maleimide-based glycogen synthase kinase-3 (GSK-3) inhibitors as stimulators of steroidogenesis

Inhibition of GSK-3β has been well documented to account for the behavioral actions of the mood stabilizer lithium in various animal models of mood disorders. Recent studies have showed that genetic or pharmacological inhibition of GSK-3β resulted in anxiolytic-like and pro-social behavior. In our ongoing efforts to develop GSK-3β inhibitors for the treatment of mood disorders, SAR studies on maleimide-based compounds were undertaken. We present herein for the first time that some of these GSK-3β inhibitors, in particular analogues 1 and 9, were able to stimulate progesterone production in the MA-10 mouse tumor Leydig cell model of steroidogenesis without any significant toxicity. These two compounds were tested in the SmartCube behavioral assay and showed anxiolytic-like signatures following daily dose administration (50 mg/kg, ip) for 13 days. Taken together, these results support the hypothesis that GSK-3β inhibition could influence neuroactive steroid production thereby mediating the modulation of anxiety-like behavior in vivo.

Lithium: the pharmacodynamic actions of the amazing ion

Lithium has been used for the treatment of mood disorders for over 60 years, yet the exact mechanisms by which it exerts its therapeutic effects remain unclear. Two enzymatic chains or pathways emerge as targets for lithium: inositol monophosphatase within the phosphatidylinositol signalling pathway and the protein kinase glycogen synthase kinase 3. Lithium inhibits these enzymes through displacing the normal cofactor magnesium, a vital regulator of numerous signalling pathways. Here we provide an overview of evidence, supporting a role for the inhibition of glycogen synthase kinase 3 and inositol monophosphatase in the pharmacodynamic actions of lithium. We also explore how inhibition of these enzymes by lithium can lead to downstream effects of clinical relevance, both for mood disorders and neurodegenerative diseases. Establishing a better understanding of lithium's mechanisms of action may allow the development of more effective and more tolerable pharmacological agents for the treatment of a range of mental illnesses, and provide clearer insight into the pathophysiology of such disorders.

The ANK3 bipolar disorder gene regulates psychiatric-related behaviors that are modulated by lithium and stress

BACKGROUND

Ankyrin 3 (ANK3) has been strongly implicated as a risk gene for bipolar disorder (BD) by recent genome-wide association studies of patient populations. However, the genetic variants of ANK3 contributing to BD risk and their pathological function are unknown.

METHODS

To gain insight into the potential disease relevance of ANK3, we examined the function of mouse Ank3 in the regulation of psychiatric-related behaviors using genetic, neurobiological, pharmacological, and gene-environment interaction (G×E) approaches. Ank3 expression was reduced in mouse brain either by viral-mediated RNA interference or through disruption of brain-specific Ank3 in a heterozygous knockout mouse.

RESULTS

RNA interference of Ank3 in hippocampus dentate gyrus induced a highly specific and consistent phenotype marked by decreased anxiety-related behaviors and increased activity during the light phase, which were attenuated by chronic treatment with the mood stabilizer lithium. Similar behavioral alterations of reduced anxiety and increased motivation for reward were also exhibited by Ank3+/- heterozygous mice compared with wild-type Ank3+/+ mice. Remarkably, the behavioral traits of Ank3+/- mice transitioned to depression-related features after chronic stress, a trigger of mood episodes in BD. Ank3+/- mice also exhibited elevated serum corticosterone, suggesting that reduced Ank3 expression is associated with elevated stress reactivity.

CONCLUSIONS

This study defines a new role for Ank3 in the regulation of psychiatric-related behaviors and stress reactivity that lends support for its involvement in BD and establishes a general framework for determining the disease relevance of genes implicated by patient genome-wide association studies.

An emerging role for Wnt and GSK3 signaling pathways in schizophrenia

Schizophrenia is a disabling illness with limited treatment options. The underlying pathophysiology remains unknown, partially due to its heterogeneous nature, and a lack of understanding of the biological functions of genetic risk factors. Several signaling pathways have been implicated, however, with the varying degrees of support. In this article, I will focus on the converging evidence supporting a prominent role for Wnt and glycogen synthase kinase 3 (GSK3) signaling in the biological bases of schizophrenia. This includes current pharmacological therapies that target GSK3, animal model and cell-based studies, and recent human genetic findings that implicate Wnt and GSK3 signaling.

Hyperactivity: glycogen synthase kinase-3 as a therapeutic target

The diagnosis of hyperactivity-associated disorders has increased within the past few years. The prevalence of hyperactivity-associated disorders is indicative of the need to more fully understand the underlying causes and to develop improved therapeutic interventions. There is increasing evidence that glycogen synthase kinase-3 (GSK3) mediates locomotor hyperactivity in a number of animal models, and therefore may be a potential target for therapeutic intervention in hyperactivity-associated behaviors. In this review, we discuss 1) the effect of manipulations of GSK3 in the absence of drugs and disorders on locomotor activity, 2) the role of GSK3 in drug-induced hyperactivity in rodents, and 3) regulation of locomotor activity by GSK3 in transgenic mouse models related to specific disorders. These studies link GSK3 regulation and activity to hyperactivity-associated behaviors and disease pathologies.

Effects of the Ras homolog Rhes on Akt/protein kinase B and glycogen synthase kinase 3 phosphorylation in striatum

G protein-coupled receptors (GPCR) signal not only through heterotrimeric G proteins, but also through alternate pathways. Thus, dopamine D2 receptors in the striatum signal through Gαi/o and also by promoting formation of a multi-protein complex containing β-arrestin2, protein phosphatase 2A (PP2A), and Akt in order to dephosphorylate Akt. Lithium, on the other hand, disrupts this complex to increase Akt phosphorylation. Rhes is a striatally enriched GTP-binding protein that has been shown to inhibit dopamine receptor-mediated behavior and signaling through heterotrimeric G proteins. Therefore, our objective was to test whether Rhes similarly affects signaling through the Akt/GSK3 pathway in the striatum. Rhes(-/-) mice showed basally increased Akt and GSK3β phosphorylation relative to rhes(+/+) mice that was not further enhanced by lithium treatment. Furthermore, they responded to the D1/D2 agonist apomorphine with increased Akt and GSK3 phosphorylation. Co-immunoprecipitation experiments revealed that apomorphine treatment recruits PP 2A-C to Akt in both rhes(+/+) and rhes(-/-) mice. Lithium did not disrupt their interaction in rhes(-/-) mice as there was little basal interaction. Rhes co-immunoprecipitated with β-arrestins, suggesting that it is integral to the multi-protein complex. Thus, Rhes is necessary for Akt dephosphorylation by the striatal multi-protein complex, and in its absence, a lithium-treated phenotype results.

GPCR Retreat 2012: timing is everything

In London, Ontario, the 13th Annual Joint meeting of the Great Lakes GPCR Retreat and the Club des Récepteurs à Sept Domaines Transmembranaires (known simply as the GPCR Retreat) was held on 17-19 October 2012, organized by Steve Ferguson and Peter Chidiac. This meeting gathered together a core group of investigators from Michigan, Ontario and Québec and has steadily increased its attendance in both the eastern (Europe) and western (USA, Canada) directions. This year's buzz naturally centered around the Nobel Prize in Chemistry, which was won the week before by Brian Kobilka and Robert Lefkowitz for their work on receptor structure and function. Michel Bouvier provided a heartfelt tribute to one of the attendees, Marc Caron, a pioneer in the GPCR field, has made many contributions to the work that led to this year's Nobel Prize. The meeting featured interesting sessions on the physiological roles of GPCRs in the nervous system, circadian biology and cancer, dealing at the cellular and molecular level with GPCR, G protein and effector structure and function, regulation and trafficking--with an overall focus on how to move molecular pharmacology in vivo.

Sphingolipids in psychiatric disorders and pain syndromes

Despite the high prevalence and devastating impact of psychiatric disorders, little is known about their etiopathology. In this review, we provide an overview on the participation of sphingolipids and enzymes responsible for their metabolism in mechanisms underlying psychiatric disorders. We focus on the pathway from sphingomyelin to proapoptotic ceramide and the subsequent metabolism of ceramide to sphingosine, which is in turn phosphorylated to yield anti-apoptotic sphingosine-1-phosphate (S1P).The sphingomyelinase/ceramide system has been linked to effects of reactive oxygen species and proinflammatory cytokines in the central nervous system as well as to synaptic transmission. Compared to ubiquitously expressed acid sphingomyelinase, acid and neutral ceramidase and neutral sphingomyelinase are highly active in brain regions. Depressed patients show elevated plasma ceramide levels and increased activities of acid sphingomyelinase which is functionally inhibited by many anti-depressive drugs. Exposure to alcohol is associated with an activation of acid and neutral sphingomyelinase observed in cell culture, mouse models and in alcohol-dependent patients and with increased concentrations of ceramide in various organs.Levels of sphingomyelin and ceramide are altered in erythrocytes and post-mortem brain tissues of schizophrenic patients in addition to changes in expression patterns for serine palmitoyltransferase and acid ceramidase leading to impaired myelination. After induction of anxiety-like behavior in animal models, higher serum levels of S1P were reported to lead to neurodegeneration. Correspondingly, S1P infusion appeared to increase anxiety-like behavior. Significantly upregulated levels of the endogenous ceramide catabolite N,N-dimethylsphingosine were observed in rat models of allodynia. Conversely, rats injected intrathecally with N,N-dimethylsphingosine developed mechanical allodynia. Moreover, S1P has been implicated in spinal nociceptive processing.The increasing interest in lipidomics and improved analytical methods led to growing insight into the connection between psychiatric and neurological disorders and sphingolipid metabolism and may once provide new targets and strategies for therapeutic intervention.

Arrestins as regulators of kinases and phosphatases

The discovery that, in addition to mediating G protein-coupled receptor (GPCR) desensitization and endocytosis, arrestins bind to diverse catalytically active nonreceptor proteins and act as ligand-regulated signaling scaffolds led to a paradigm shift in the study of GPCR signal transduction. Research over the past decade has solidified the concept that arrestins confer novel GPCR-signaling capacity by recruiting protein and lipid kinase, phosphatase, phosphodiesterase, and ubiquitin ligase activity into receptor-based multiprotein "signalsome" complexes. Signalsomes regulate downstream pathways controlled by Src family nonreceptor tyrosine kinases, mitogen-activated protein kinases, protein kinase B (AKT), glycogen synthase kinase 3, protein phosphatase 2A, nuclear factor-κB, and several others, imposing spatial and temporal control on their function. While many arrestin-bound kinases and phosphatases are involved in the control of cytoskeletal rearrangement, vesicle endocytosis, exocytosis, and cell migration, other signals reach into the nucleus, affecting cell proliferation, apoptosis, and survival. Indeed, the kinase/phosphatase network regulated by arrestins may be fully as diverse as that regulated by heterotrimeric G proteins.

Therapeutic potential of mood stabilizers lithium and valproic acid: beyond bipolar disorder

The mood stabilizers lithium and valproic acid (VPA) are traditionally used to treat bipolar disorder (BD), a severe mental illness arising from complex interactions between genes and environment that drive deficits in cellular plasticity and resiliency. The therapeutic potential of these drugs in other central nervous system diseases is also gaining support. This article reviews the various mechanisms of action of lithium and VPA gleaned from cellular and animal models of neurologic, neurodegenerative, and neuropsychiatric disorders. Clinical evidence is included when available to provide a comprehensive perspective of the field and to acknowledge some of the limitations of these treatments. First, the review describes how action at these drugs' primary targets--glycogen synthase kinase-3 for lithium and histone deacetylases for VPA--induces the transcription and expression of neurotrophic, angiogenic, and neuroprotective proteins. Cell survival signaling cascades, oxidative stress pathways, and protein quality control mechanisms may further underlie lithium and VPA's beneficial actions. The ability of cotreatment to augment neuroprotection and enhance stem cell homing and migration is also discussed, as are microRNAs as new therapeutic targets. Finally, preclinical findings have shown that the neuroprotective benefits of these agents facilitate anti-inflammation, angiogenesis, neurogenesis, blood-brain barrier integrity, and disease-specific neuroprotection. These mechanisms can be compared with dysregulated disease mechanisms to suggest core cellular and molecular disturbances identifiable by specific risk biomarkers. Future clinical endeavors are warranted to determine the therapeutic potential of lithium and VPA across the spectrum of central nervous system diseases, with particular emphasis on a personalized medicine approach toward treating these disorders.

Selective deletion of forebrain glycogen synthase kinase 3β reveals a central role in serotonin-sensitive anxiety and social behaviour

Serotonin (5-HT) neurotransmission is thought to underlie mental illnesses, such as bipolar disorder, depression, autism and schizophrenia. Independent studies have indicated that 5-HT or drugs acting on 5-HT neurotransmission regulate the serine/threonine kinase glycogen synthase kinase 3β (GSK3β). Furthermore, GSK3β inhibition rescues behavioural abnormalities in 5-HT-deficient mice with a loss-of-function mutation equivalent to the human variant (R441H) of tryptophan hydroxylase 2. In an effort to define neuroanatomical correlates of GSK3β activity in the regulation of behaviour, we generated CamKIIcre-floxGSK3β mice in which the gsk3b gene is postnatally inactivated in forebrain pyramidal neurons. Behavioural characterization showed that suppression of GSK3β in these brain areas has anxiolytic and pro-social effects. However, while a global reduction of GSK2β expression reduced responsiveness to amphetamine and increased resilience to social defeat, these behavioural effects were not found in CamKIIcre-floxGSK3β mice. These findings demonstrate a dissociation of behavioural effects related to GSK3 inhibition, with forebrain GSK3β being involved in the regulation of anxiety and sociability while social preference, resilience and responsiveness to psychostimulants would involve a function of this kinase in subcortical areas such as the hippocampus and striatum.

β-arrestin 2 regulates Aβ generation and γ-secretase activity in Alzheimer's disease

β-arrestins are associated with numerous aspects of G protein-coupled receptor (GPCR) signaling and regulation and accordingly influence diverse physiological and pathophysiological processes. Here we report that β-arrestin 2 expression is elevated in two independent cohorts of individuals with Alzheimer's disease. Overexpression of β-arrestin 2 leads to an increase in amyloid-β (Aβ) peptide generation, whereas genetic silencing of Arrb2 (encoding β-arrestin 2) reduces generation of Aβ in cell cultures and in Arrb2(-/-) mice. Moreover, in a transgenic mouse model of Alzheimer's disease, genetic deletion of Arrb2 leads to a reduction in the production of Aβ(40) and Aβ(42). Two GPCRs implicated previously in Alzheimer's disease (GPR3 and the β(2)-adrenergic receptor) mediate their effects on Aβ generation through interaction with β-arrestin 2. β-arrestin 2 physically associates with the Aph-1a subunit of the γ-secretase complex and redistributes the complex toward detergent-resistant membranes, increasing the catalytic activity of the complex. Collectively, these studies identify β-arrestin 2 as a new therapeutic target for reducing amyloid pathology and GPCR dysfunction in Alzheimer's disease.

Activation of GABA(B) receptors inhibits protein kinase B/glycogen synthase kinase 3 signaling

Accumulated evidence has suggested that potentiation of cortical GABAergic inhibitory neurotransmission may be a key mechanism in the treatment of schizophrenia. However, the downstream molecular mechanisms related to GABA potentiation remain unexplored. Recent studies have suggested that dopamine D2 receptor antagonists, which are used in the clinical treatment of schizophrenia, modulate protein kinase B (Akt)/glycogen synthase kinase (GSK)-3 signaling. Here we report that activation of GABA_B receptors significantly inhibits Akt/GSK-3 signaling in a β-arrestin-dependent pathway. Agonist stimulation of GABA_B receptors enhances the phosphorylation of Akt (Thr-308) and enhances the phosphorylation of GSK-3α (Ser-21)/β (Ser-9) in both HEK-293T cells expressing GABA_B receptors and rat hippocampal slices. Furthermore, knocking down the expression of β-arrestin2 using siRNA abolishes the GABA_B receptor-mediated modulation of GSK-3 signaling. Our data may help to identify potentially novel targets through which GABA_B receptor agents may exert therapeutic effects in the treatment of schizophrenia.

Deletion of GSK3β in D2R-expressing neurons reveals distinct roles for β-arrestin signaling in antipsychotic and lithium action

Several studies in rodent models have shown that glycogen synthase kinase 3 β (GSK3β) plays an important role in the actions of antispychotics and mood stabilizers. Recently it was demonstrated that GSK3β through a β-arrestin2/protein kinase B (PKB or Akt)/protein phosphatase 2A (PP2A) signaling complex regulates dopamine (DA)- and lithium-sensitive behaviors and is required to mediate endophenotypes of mania and depression in rodents. We have previously shown that atypical antipsychotics antagonize DA D2 receptor (D2R)/β-arrestin2 interactions more efficaciously than G-protein-dependent signaling, whereas typical antipsychotics inhibit both pathways with similar efficacy. To elucidate the site of action of GSK3β in regulating DA- or lithium-sensitive behaviors, we generated conditional knockouts of GSK3β, where GSK3β was deleted in either DA D1- or D2-receptor-expressing neurons. We analyzed these mice for behaviors commonly used to test antipsychotic efficacy or behaviors that are sensitive to lithium treatment. Mice with deletion of GSK3β in D2 (D2GSK3β(-/-)) but not D1 (D1GSK3β(-/-)) neurons mimic antipsychotic action. However, haloperidol (HAL)-induced catalepsy was unchanged in either D2GSK3β(-/-) or D1GSK3β(-/-) mice compared with control mice. Interestingly, genetic stabilization of β-catenin, a downstream target of GSK3β, in D2 neurons did not affect any of the behaviors tested. Moreover, D2GSK3β(-/-) or D1GSK3β(-/-) mice showed similar responses to controls in the tail suspension test (TST) and dark-light emergence test, behaviors which were previously shown to be β-arrestin2- and GSK3β-dependent and sensitive to lithium treatment. Taken together these studies suggest that selective deletion of GSK3β but not stabilization of β-catenin in D2 neurons mimics antipsychotic action without affecting signaling pathways involved in catalepsy or certain mood-related behaviors.

Nemo-like kinase, a multifaceted cell signaling regulator

Nemo-like kinase (NLK) is an evolutionarily conserved MAP kinase-related kinase. Although NLK was originally identified as a Drosophila gene affecting cell movement during eye development, recent studies show that NLK also contributes to cell proliferation, differentiation, and morphological changes during early embryogenesis and nervous system development in vertebrates. In addition, NLK has been reported to be involved in the development of several human cancers. NLK is able to play a role in multiple processes due to its capacity to regulate a diverse array of signaling pathways, including the Wnt/β-catenin, Activin, IL-6, and Notch signaling pathways. Although the molecular mechanisms that regulate NLK activity remain unclear, our recent research has presented a new model for NLK activation. Here, we summarize the current understanding of the function and regulation of NLK and discuss the aspects of NLK regulation that remain to be resolved.

The wnt pathway in mood disorders

OBJECTIVES

To review the evidence of the involvement of the Wnt signalling pathway in mood disorders and in the action of drugs used to treat these disorders.

METHODS

We performed a careful PubMed search using as keywords all possible terms relevant to the Wnt pathway and crossing them with each of four areas, i.e., developmental effects, behavioural effects, mood disorders, and drugs used in their treatment. Papers were selected on the basis of their content and their data used for discussion.

RESULTS

Neurodevelopmental and behavioural data point to the possibility of involvement of the Wnt pathway in the pathophysiology of mood disorders. Clinical and post-mortem data are not sufficient to corroborate a definite role for Wnt alterations in any mood disorder. Combining genetic and pharmacological data, we may state that glycogen synthase kinase is the key molecule in bipolar disorder, as it is connected with many other signalling pathways that were shown to be involved in mood disorders, while Wnt molecules in the hippocampus appear to be mainly involved in depressive disorders.

CONCLUSIONS

Altered Wnt signalling may play a role in the pathophysiology of mood disorders, although not a central one. It is premature to draw conclusions regarding the possible usefulness of Wnt manipulations in the treatment of mood disorders.

The effects of glycogen synthase kinase-3beta in serotonin neurons

Glycogen synthase kinase-3 (GSK3) is a constitutively active protein kinase in brain. Increasing evidence has shown that GSK3 acts as a modulator in the serotonin neurotransmission system, including direct interaction with serotonin 1B (5-HT1B) receptors in a highly selective manner and prominent modulating effect on 5-HT1B receptor activity. In this study, we utilized the serotonin neuron-selective GSK3β knockout (snGSK3β-KO) mice to test if GSK3β in serotonin neurons selectively modulates 5-HT1B autoreceptor activity and function. The snGSK3β-KO mice were generated by crossbreeding GSK3β-floxed mice and ePet1-Cre mice. These mice had normal growth and physiological characteristics, similar numbers of tryptophan hydroxylase-2 (TpH2)-expressing serotonin neurons, and the same brain serotonin content as in littermate wild type mice. However, the expression of GSK3β in snGSK3β-KO mice was diminished in TpH2-expressing serotonin neurons. Compared to littermate wild type mice, snGSK3β-KO mice had a reduced response to the 5-HT1B receptor agonist anpirtoline in the regulation of serotonergic neuron firing, cAMP production, and serotonin release, whereas these animals displayed a normal response to the 5-HT1A receptor agonist 8-OH-DPAT. The effect of anpirtoline on the horizontal, center, and vertical activities in the open field test was differentially affected by GSK3β depletion in serotonin neurons, wherein vertical activity, but not horizontal activity, was significantly altered in snGSK3β-KO mice. In addition, there was an enhanced anti-immobility response to anpirtoline in the tail suspension test in snGSK3β-KO mice. Therefore, results of this study demonstrated a serotonin neuron-targeting function of GSK3β by regulating 5-HT1B autoreceptors, which impacts serotonergic neuron firing, serotonin release, and serotonin-regulated behaviors.

Regional differences in human ependymal and subventricular zone cytoarchitecture are unchanged in neuropsychiatric disease

Much work has focused on the possible contribution of adult hippocampal neurogenesis to neuropsychiatric diseases. The hippocampal subgranular zone and the other stem cell-containing neurogenic niche, the subventricular zone (SVZ), share several cytological features and are regulated by some of the same molecular mechanisms. However, very little is known about the SVZ in neuropsychiatric disorders. This is important since it surrounds the lateral ventricles and in schizophrenia ventricular enlargement frequently follows forebrain nuclei shrinkage. Also, adult neurogenesis has been implicated in pharmacotherapy for affective disorders and many of the molecules associated with neuropsychiatric disorders affect SVZ biology. To assess the neurogenic niche, we examined material from 60 humans (Stanley Collection) and characterized the cytoarchitecture of the SVZ and ependymal layer in age-, sex- and post mortem interval-matched controls, and patients diagnosed with schizophrenia, bipolar illness, and depression (n = 15 each). There is a paucity of post mortem brains available for study in these diseases, so to maximize the number of possible parameters examined here, we quantified individual sections rather than a large series. Previous work showed that multiple sclerosis is associated with increased width of the hypocellular gap, a cell-sparse region that typifies the human SVZ. Statistically there were no differences between disease groups and controls in the width of the hypocellular gap or in the density of cells in the hypocellular gap. Because ventricular enlargement in schizophrenia may disrupt ependymal cells, we quantified them, but observed no difference between diagnostic groups and controls. There are significant differences in the prevalence of neuropsychiatric illness between the sexes. Therefore, we looked for male versus female differences, but did not observe any in the parameters quantified. We next turned to a finer spatial resolution and asked if there were differences amongst the disease groups in dorsal ventral subdivisions of the SVZ. Similar to when we treated the SVZ as a whole, we did not find such differences. However, compared to the dorsal SVZ, the ventral SVZ had a wider hypocellular gap and more ependymal cells in all four groups. In contrast, cell density was similar in dorsal ventral subregions of the SVZ hypocellular gap. These results show that though there are regional differences in the SVZ in humans, neuropsychiatric disorders do not seem to alter several fundamental histological features of this adult neurogenic zone.

Hypothesis review: are clathrin-mediated endocytosis and clathrin-dependent membrane and protein trafficking core pathophysiological processes in schizophrenia and bipolar disorder?

Clathrin-mediated endocytosis (CME) is the best-characterized mechanism governing cellular membrane and protein trafficking. In this hypothesis review, we integrate recent evidence implicating CME and related cellular trafficking mechanisms in the pathophysiology of psychotic disorders such as schizophrenia and bipolar disorder. The evidence includes proteomic and genomic findings implicating proteins and genes of the clathrin interactome. Additionally, several important candidate genes for schizophrenia, such as dysbindin, are involved in processes closely linked to CME and membrane trafficking. We discuss that key aspects of psychosis neuropathology such as synaptic dysfunction, white matter changes and aberrant neurodevelopment are all influenced by clathrin-dependent processes, and that other cellular trafficking mechanisms previously linked to psychoses interact with the clathrin interactome in important ways. Furthermore, many antipsychotic drugs have been shown to affect clathrin-interacting proteins. We propose that the targeted pharmacological manipulation of the clathrin interactome may offer fruitful opportunities for novel treatments of schizophrenia.

Brain region differences in regulation of Akt and GSK3 by chronic stimulant administration in mice

Acute amphetamine administration activates glycogen synthase kinase-3 (GSK3) by reducing its inhibitory serine-phosphorylation in mouse striatum and cerebral cortex. This results from Akt inactivation and is required for certain behavioral effects of amphetamine, such as increased locomotor activity. Here we tested if regulation of Akt and GSK3 was similarly affected by longer-term administration of amphetamine, as well as of methylphenidate, since each of these is administered chronically in patients with attention deficit hyperactivity disorder (ADHD). Akt is activated by post-translational phosphorylation on Thr308, and modulated by Ser473 phosphorylation, whereas phosphorylation on Ser21/9 inhibits the two GSK3 isoforms, GSK3α and GSK3β. After eight days of amphetamine or methylphenidate treatment, striatal Akt and GSK3 were dephosphorylated similar to reported changes after acute amphetamine treatment. Oppositely, in the cerebral cortex and hippocampus Akt and GSK3 phosphorylation increased after eight days of amphetamine or methylphenidate treatment. These opposite brain region changes in Akt and GSK3 phosphorylation matched opposite changes in the association of Akt with β-arrestin and GSK3, which after eight days of amphetamine treatment were increased in the striatum and decreased in the cerebral cortex. Thus, whereas the acute dephosphorylating effect of stimulants on Akt and GSK3 in the striatum was maintained, the response switched in the cerebral cortex after eight days of amphetamine or methylphenidate treatment to cause increased phosphorylation of Akt and GSK3. These results demonstrate that prolonged administration of stimulants causes brain region-selective differences in the regulation of Akt and GSK3.

The pharmacogenomics of mood stabilizer response in bipolar disorder

Bipolar Disorder (BD) is a common psychiatric illness that has a recurring course and 17% - 24% lifetime prevalence of suicide attempts. Difficulty in diagnosis and individual variation in response point to a great need for personalized medicine. Studies to date have focused largely on lithium and suggest the idea that different medication responses may reflect different disease mechanisms. An overview of current pharmacogenomic studies will be presented and needs and future directions discussed.

Inhibition of GSK3 by lithium, from single molecules to signaling networks

For more than 60 years, the mood stabilizer lithium has been used alone or in combination for the treatment of bipolar disorder, schizophrenia, depression, and other mental illnesses. Despite this long history, the molecular mechanisms trough which lithium regulates behavior are still poorly understood. Among several targets, lithium has been shown to directly inhibit glycogen synthase kinase 3 alpha and beta (GSK3α and GSK3β). However in vivo, lithium also inhibits GSK3 by regulating other mechanisms like the formation of a signaling complex comprised of beta-arrestin 2 (βArr2) and Akt. Here, we provide an overview of in vivo evidence supporting a role for inhibition of GSK3 in some behavioral effects of lithium. We also explore how regulation of GSK3 by lithium within a signaling network involving several molecular targets and cell surface receptors [e.g., G protein coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs)] may provide cues to its relative pharmacological selectivity and its effects on disease mechanisms. A better understanding of these intricate actions of lithium at a systems level may allow the rational development of better mood stabilizer drugs with enhanced selectivity, efficacy, and lesser side effects.

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.

Common DISC1 polymorphisms disrupt Wnt/GSK3β signaling and brain development

Disrupted in Schizophrenia-1 (DISC1) is a candidate gene for psychiatric disorders and has many roles during brain development. Common DISC1 polymorphisms (variants) are associated with neuropsychiatric phenotypes including altered cognition, brain structure, and function; however, it is unknown how this occurs. Here, we demonstrate using mouse, zebrafish, and human model systems that DISC1 variants are loss of function in Wnt/GSK3β signaling and disrupt brain development. The DISC1 variants A83V, R264Q, and L607F, but not S704C, do not activate Wnt signaling compared with wild-type DISC1 resulting in decreased neural progenitor proliferation. In zebrafish, R264Q and L607F could not rescue DISC1 knockdown-mediated aberrant brain development. Furthermore, human lymphoblast cell lines endogenously expressing R264Q displayed impaired Wnt signaling. Interestingly, S704C inhibited the migration of neurons in the developing neocortex. Our data demonstrate DISC1 variants impair Wnt signaling and brain development and elucidate a possible mechanism for their role in neuropsychiatric phenotypes.

Prolyl oligopeptidase, inositol phosphate signalling and lithium sensitivity

Inhibition of prolyl oligopeptidase (PO) elevates inositol phosphate (IP) signalling and reduces cell sensitivity to lithium (Li⁺). This review discusses recent evidence that shows PO acts via the multiple inositol polyphosphate phosphatase (MIPP) to regulate gene expression. As a consequence, PO inhibition causes both a transient, rapid increase in I(1,4,5)P₃ and a long-term elevation of IP signalling. This pathway is evolutionary conserved, being present in both the social amoeba Dictyostelium and human cell systems, and has potential implications for mental health.

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.

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.

Beyond cAMP: The Regulation of Akt and GSK3 by Dopamine Receptors

Brain dopamine receptors have been preferred targets for numerous pharmacological compounds developed for the treatment of various neuropsychiatric disorders. Recent discovery that D2 dopamine receptors, in addition to cAMP pathways, can engage also in Akt/GSK3 signaling cascade provided a new framework to understand intracellular signaling mechanisms involved in dopamine-related behaviors and pathologies. Here we review a recent progress in understanding the role of Akt, GSK3, and related signaling molecules in dopamine receptor signaling and functions. Particularly, we focus on the molecular mechanisms involved, interacting partners, role of these signaling events in the action of antipsychotics, psychostimulants, and antidepressants as well as involvement in pathophysiology of schizophrenia, bipolar disorder, and Parkinson’s disease. Further understanding of the role of Akt/GSK3 signaling in dopamine receptor functions could provide novel targets for pharmacological interventions in dopamine-related disorders.

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.

Discovery of β-arrestin-biased dopamine D2 ligands for probing signal transduction pathways essential for antipsychotic efficacy

Elucidating the key signal transduction pathways essential for both antipsychotic efficacy and side-effect profiles is essential for developing safer and more effective therapies. Recent work has highlighted noncanonical modes of dopamine D(2) receptor (D(2)R) signaling via β-arrestins as being important for the therapeutic actions of both antipsychotic and antimanic agents. We thus sought to create unique D(2)R agonists that display signaling bias via β-arrestin-ergic signaling. Through a robust diversity-oriented modification of the scaffold represented by aripiprazole (1), we discovered UNC9975 (2), UNC0006 (3), and UNC9994 (4) as unprecedented β-arrestin-biased D(2)R ligands. These compounds also represent unprecedented β-arrestin-biased ligands for a G(i)-coupled G protein-coupled receptor (GPCR). Significantly, UNC9975, UNC0006, and UNC9994 are simultaneously antagonists of G(i)-regulated cAMP production and partial agonists for D(2)R/β-arrestin-2 interactions. Importantly, UNC9975 displayed potent antipsychotic-like activity without inducing motoric side effects in inbred C57BL/6 mice in vivo. Genetic deletion of β-arrestin-2 simultaneously attenuated the antipsychotic actions of UNC9975 and transformed it into a typical antipsychotic drug with a high propensity to induce catalepsy. Similarly, the antipsychotic-like activity displayed by UNC9994, an extremely β-arrestin-biased D(2)R agonist, in wild-type mice was completely abolished in β-arrestin-2 knockout mice. Taken together, our results suggest that β-arrestin signaling and recruitment can be simultaneously a significant contributor to antipsychotic efficacy and protective against motoric side effects. These functionally selective, β-arrestin-biased D(2)R ligands represent valuable chemical probes for further investigations of D(2)R signaling in health and disease.

Glycogen synthase kinase 3 involvement in the excessive proinflammatory response to LPS in patients with decompensated cirrhosis

BACKGROUND & AIMS

In decompensated cirrhosis, the early innate immune response to the Toll-like receptor 4 (TLR4) agonist, lipopolysaccharides (LPS), is characterized by a hyper-production of pro-inflammatory cytokines and hypo-production of the anti-inflammatory cytokine IL-10. In LPS-stimulated non-cirrhotic immune cells, the constitutively active glycogen synthase kinase (GSK) 3 favors pro- vs. anti-inflammatory cytokines, by acting on gene induction. However, in these cells, TLR4 dampens its own pro-inflammatory response by inducing early (within minutes) AKT-mediated phosphorylation of GSK3β (one of two GSK3 isoforms) on Ser9. Phosphorylation of GSK3β (Ser9) inhibits its activity, decreases pro-inflammatory cytokines, and increases IL-10. Thus, we investigated the role of GSK3 in LPS-induced cytokine production by peripheral blood mononuclear cells (PBMCs) or monocytes from patients with advanced cirrhosis and normal subjects.

METHODS

Cells were pre-incubated with or without GSK3 inhibitor (SB216763 or lithium chloride) for 1h and then stimulated with LPS. Cytokine production was assessed at mRNA and secreted proteins levels, by real-time RT-PCR at 1h and ELISA at 20 h, respectively. GSK3β phosphorylation was assessed using Western blotting.

RESULTS

In cirrhotic and normal PBMCs pretreated with GSK3 inhibitors, LPS-induced production of pro-inflammatory proteins TNF-α and IL-12p40 was significantly decreased while that of IL-10 was increased. LPS-induced, AKT-mediated phosphorylation of GSK3β on Ser9 found in normal monocytes, was abolished in cirrhotic cells.

CONCLUSIONS

GSK3 is involved in the early TLR4-mediated pro-inflammatory response in patients with decompensated cirrhosis. This was associated with a defect in AKT-mediated GSK3β phosphorylation resulting in unrestricted 'pro-inflammatory' activity of the enzyme.

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.

Role of Beta-arrestin 2 downstream of dopamine receptors in the Basal Ganglia

Multifunctional scaffolding protein beta-arrestins (βArr) and the G protein-receptor kinases are involved in the desensitization of several G protein-coupled receptors (GPCR). However, arrestins can also contribute to GPCR signaling independently from G proteins. In this review, we focus on the role of βArr in the regulation of dopamine receptor functions in the striatum. First, we present in vivo evidence supporting a role for these proteins in the regulation of dopamine receptor desensitization. Second, we provide an overview of the roles of βArr2 in the regulation of extracellular-signal-regulated kinases/MAP kinases and Akt/GSK3 signaling pathways downstream of the D1 and D2 dopamine receptors. Thereafter, we examine the possible involvement of βArr-mediated signaling in the action of dopaminergic drugs used for the treatment of mental disorders. Finally, we focus on different potential cellular proteins regulated by βArr-mediated signaling which could contribute to the regulation of behavioral responses to dopamine. Overall, the identification of a cell signaling function for βArr downstream of dopamine receptors underscores the intricate complexity of the intertwined mechanisms regulating and mediating cell signaling in the basal ganglia. Understanding these mechanisms may lead to a better comprehension of the several roles played by these structures in the regulation of mood and to the development of new psychoactive drugs having better therapeutic efficacy.

DISC1 regulates synaptic vesicle transport via a lithium-sensitive pathway

Disrupted-in-Schizophrenia 1 (DISC1) is a susceptibility gene for major mental illnesses, including bipolar disorder and schizophrenia. Although the roles of DISC1 in nervous system development and functions are increasingly recognized, pathophysiological mechanisms underlying a range of neuropsychiatric symptoms caused by DISC1 mutations remain unclear. Here we show that DISC1 enhances synaptic vesicle transport along microtubules. Knocking down DISC1 expression results in attenuated vesicle transport in primary cortical neurons. Likewise, expressing the dominant-negative, breakpoint mutant version of DISC1 causes defective vesicle transport, by disrupting the assembly between the kinesin-1 adaptor FEZ1 and the cargo protein Synaptotagmin-1 (Syt-1). In addition, lithium, a mood-stabilizing agent used for the treatment of bipolar disorder, can restore the assembly of FEZ1 and Syt-1, and normalizes the defective transport caused by the dominant-negative DISC1. Thus, this study addresses a new role of DISC1 in organelle transport in neurons, and suggests that this cellular pathway could be therapeutically targeted for the treatment against neuropsychiatric diseases.

Functional selectivity at the μ-opioid receptor: implications for understanding opioid analgesia and tolerance

Opioids are the most effective analgesic drugs for the management of moderate or severe pain, yet their clinical use is often limited because of the onset of adverse side effects. Drugs in this class produce most of their physiological effects through activation of the μ opioid receptor; however, an increasing number of studies demonstrate that different opioids, while presumably acting at this single receptor, can activate distinct downstream responses, a phenomenon termed functional selectivity. Functional selectivity of receptor-mediated events can manifest as a function of the drug used, the cellular or neuronal environment examined, or the signaling or behavioral measure recorded. This review summarizes both in vitro and in vivo work demonstrating functional selectivity at the μ opioid receptor in terms of G protein coupling, receptor phosphorylation, interactions with β-arrestins, receptor desensitization, internalization and signaling, and details on how these differences may relate to the progression of analgesic tolerance after their extended use.

Inositol pyrophosphates as mammalian cell signals

Inositol pyrophosphates are highly energetic inositol polyphosphate molecules present in organisms from slime molds and yeast to mammals. Distinct classes of enzymes generate different forms of inositol pyrophosphates. The biosynthesis of these substances principally involves phosphorylation of inositol hexakisphosphate (IP₆) to generate the pyrophosphate IP₇. Initial insights into functions of these substances derived primarily from yeast, which contain a single isoform of IP₆ kinase (yIP₆K), as well as from the slime mold Dictyostelium. Mammalian functions for inositol pyrophosphates have been investigated by using cell lines to establish roles in various processes, including insulin secretion and apoptosis. More recently, mice with targeted deletion of IP₆K isoforms as well as the related inositol polyphosphate multikinase (IPMK) have substantially enhanced our understanding of inositol polyphosphate physiology. Phenotypic alterations in mice lacking inositol hexakisphosphate kinase 1 (IP₆K1) reveal signaling roles for these molecules in insulin homeostasis, obesity, and immunological functions. Inositol pyrophosphates regulate these processes at least in part by inhibiting activation of the serine-threonine kinase Akt. Similar studies of IP₆K2 establish this enzyme as a cell death inducer acting by stimulating the proapoptotic protein p53. IPMK is responsible for generating the inositol phosphate IP₅ but also has phosphatidylinositol 3-kinase activity--that participates in activation of Akt. Here, we discuss recent advances in understanding the physiological functions of the inositol pyrophosphates based in substantial part on studies in mice with deletion of IP₆K isoforms. These findings highlight the interplay of IPMK and IP₆K in regulating growth factor and nutrient-mediated cell signaling.

Glycogen synthase kinase-3 in the etiology and treatment of mood disorders

The mood disorders major depressive disorder and bipolar disorder are prevalent, are inadequately treated, and little is known about their etiologies. A better understanding of the causes of mood disorders would benefit from improved animal models of mood disorders, which now rely on behavioral measurements. This review considers the limitations in relating measures of rodent behaviors to mood disorders, and the evidence from behavioral assessments indicating that glycogen synthase kinase-3 (GSK3) dysregulation promotes mood disorders and is a potential target for treating mood disorders. The classical mood stabilizer lithium was identified by studying animal behaviors and later was discovered to be an inhibitor of GSK3. Several mood-relevant behavioral effects of lithium in rodents have been identified, and most have now been shown to be due to its inhibition of GSK3. An extensive variety of pharmacological and molecular approaches for manipulating GSK3 are discussed, the results of which strongly support the proposal that inhibition of GSK3 reduces both depression-like and manic-like behaviors. Studies in human postmortem brain and peripheral cells also have identified correlations between alterations in GSK3 and mood disorders. Evidence is reviewed that depression may be associated with impaired inhibitory control of GSK3, and mania by hyper-stimulation of GSK3. Taken together, these studies provide substantial support for the hypothesis that inhibition of GSK3 activity is therapeutic for mood disorders. Future research should identify the causes of dysregulated GSK3 in mood disorders and the actions of GSK3 that contribute to these diseases.

Glycogen synthase kinase-3 is essential for β-arrestin-2 complex formation and lithium-sensitive behaviors in mice

Lithium is the first-line therapy for bipolar disorder. However, its therapeutic target remains controversial. Candidates include inositol monophosphatases, glycogen synthase kinase-3 (GSK-3), and a β-arrestin-2/AKT/protein phosphatase 2A (β-arrestin-2/AKT/PP2A) complex that is known to be required for lithium-sensitive behaviors. Defining the direct target(s) is critical for the development of new therapies and for elucidating the molecular pathogenesis of this major psychiatric disorder. Here, we show what we believe to be a new link between GSK-3 and the β-arrestin-2 complex in mice and propose an integrated mechanism that accounts for the effects of lithium on multiple behaviors. GSK-3β (Gsk3b) overexpression reversed behavioral defects observed in lithium-treated mice and similar behaviors observed in Gsk3b+/- mice. Furthermore, immunoprecipitation of striatial tissue from WT mice revealed that lithium disrupted the β-arrestin-2/Akt/PP2A complex by directly inhibiting GSK-3. GSK-3 inhibitors or loss of one copy of the Gsk3b gene reduced β-arrestin-2/Akt/PP2A complex formation in mice, while overexpression of Gsk3b restored complex formation in lithium-treated mice. Thus, GSK-3 regulates the stability of the β-arrestin-2/Akt/PP2A complex, and lithium disrupts the complex through direct inhibition of GSK-3. We believe these findings reveal a new role for GSK-3 within the β-arrestin complex and demonstrate that GSK-3 is a critical target of lithium in mammalian behaviors.

Dysfunction of endothelium-dependent relaxation to insulin via PKC-mediated GRK2/Akt activation in aortas of ob/ob mice

In diabetic states, hyperinsulinemia may negatively regulate Akt/endothelial nitric oxide synthase (eNOS) activation. Our main aim was to investigate whether and how insulin might negatively regulate Akt/eNOS activities via G protein-coupled receptor kinase 2 (GRK2) in aortas from ob/ob mice. Endothelium-dependent relaxation was measured in aortic rings from ob/ob mice (a type 2 diabetes model). GRK2, β-arrestin2, and Akt/eNOS signaling-pathway protein levels and activities were mainly assayed by Western blotting. Plasma insulin was significantly elevated in ob/ob mice. Insulin-induced relaxation was significantly decreased in the ob/ob aortas [vs. age-matched control (lean) ones]. The response in ob/ob aortas was enhanced by PKC inhibitor or GRK2 inhibitor. Akt (at Thr308) phosphorylation and eNOS (at Ser1177) phosphorylation, and also the β-arrestin2 protein level, were markedly decreased in the membrane fraction of insulin-stimulated ob/ob aortas (vs. insulin-stimulated lean ones). These membrane-fraction expressions were enhanced by GRK2 inhibitor and by PKC inhibitor in the ob/ob group but not in the lean group. PKC activity was much greater in ob/ob than in lean aortas. GRK2 protein and activity levels were increased in ob/ob and were greatly reduced by GRK2 inhibitor or PKC inhibitor pretreatment. These results suggest that in the aorta in diabetic mice with hyperinsulinemia an upregulation of GRK2 and a decrease in β-arrestin2 inhibit insulin-induced stimulation of the Akt/eNOS pathway and that GRK2 overactivation may result from an increase in PKC activity.

The role of dopaminergic signalling during larval zebrafish brain development: a tool for investigating the developmental basis of neuropsychiatric disorders

Neurodevelopment depends on intrinsic and extrinsic factors that influence the overall pattern of neurogenesis and neural circuit formation, which has a direct impact on behaviour. Defects in dopamine signalling and brain morphology at a relatively early age, and mutations in neurodevelopmental genes are strongly correlated with several neuropsychiatric disorders. This evidence supports the hypothesis of a neurodevelopmental origin of at least some forms of mental illness. Zebrafish (Danio rerio) has emerged as an important vertebrate model system in biomedical research. The ease with which intrinsic and extrinsic factors can be altered during early development, the relatively conserved dopaminergic circuit organisation in the larval brain, and the emergence of simple sensorimotor behaviours very early in development are some of the appealing features that make this organism advantageous for developmental brain and behaviour research. Thus, examining the impact of altered dopamine signalling and disease related genetic aberrations during zebrafish development presents a unique opportunity to holistically analyse the in vivo biochemical, morphological and behavioural significance of altered dopamine signalling during a crucial period of development using a highly tractable vertebrate model organism. Ultimately, this information will shed new light on potential therapeutic targets for the treatment of schizophrenia and perhaps serve as a paradigm for investigating the neurodevelopmental origin of other psychiatric disorders.