Comparison of inflammatory and behavioral responses to chronic stress in female and male mice

Major depressive disorder (MDD) is a debilitating disease with a high worldwide prevalence. Despite its greater prevalence in women, male animals are used in most preclinical studies of depression even though there are many sex differences in key components of depression, such as stress responses and immune system functions. In the present study, we found that chronic restraint stress-induced depressive-like behaviors are quite similar in male and female mice, with both sexes displaying increased immobility time in the tail suspension test and reduced social interactions, and both sexes exhibited deficits in working and spatial memories. However, in contrast to the similar depressive-like behaviors developed by male and female mice in response to stress, they displayed different patterns of pro-inflammatory cytokine increases in the periphery and the brain, different changes in microglia, and different changes in the expression of Toll-like receptor 4 in response to stress. Treatment with (+)-naloxone, a Toll-like receptor 4 antagonist that previously demonstrated anti-depressant-like effects in male mice, was more efficacious in male than female mice in reducing the deleterious effects of stress, and its effects were not microbiome-mediated. Altogether, these results suggest differential mechanisms to consider in potential sex-specific treatments of depression.

Targeting the Adaptive Immune System in Depression: Focus on T Helper 17 Cells

There is a vital need to understand mechanisms contributing to susceptibility to depression to improve treatments for the 11% of Americans who currently suffer from this debilitating disease. The adaptive immune system, comprising T and B cells, has emerged as a potential contributor to depression, as demonstrated in the context of lymphopenic mice. Overall, patients with depression have reduced circulating T and regulatory B cells, "immunosuppressed" T cells, and alterations in the relative abundance of T cell subtypes. T helper (Th) cells have the capacity to differentiate to various lineages depending on the cytokine environment, antigen stimulation, and costimulation. Regulatory T cells are decreased, and the Th1/Th2 ratio and the Th17 cells are increased in patients with depression. Evidence for changes in each Th lineage has been reported to some extent in patients with depression. However, the evidence is strongest for the association of depression with changes in Th17 cells. Th17 cells produce the inflammatory cytokine interleukin (IL)-17A, and the discovery of Th17 cell involvement in depression evolved from the well established link that IL-6, which is required for Th17 cell differentiation, contributes to the onset, and possibly maintenance, of depression. One intriguing action of Th17 cells is their participation in the gut-brain axis to mediate stress responses. Although the mechanisms of action of Th17 cells in depression remain unclear, neutralization of IL-17A by anti-IL-17A antibodies, blocking stress-induced production, or release of gut Th17 cells represent feasible therapeutic approaches and might provide a new avenue to improve depression symptoms. SIGNIFICANCE STATEMENT: Th17 cells appear as a promising therapeutic target for depression, for which efficacious therapeutic options are limited. The use of neutralizing antibodies targeting Th17 cells has provided encouraging results in depressed patients with comorbid autoimmune diseases.

Effects of (+)-naloxone blocking Toll-like Receptor 4 in depression and cognition

The immune system has been shown to affect the brain, and consequently behaviors. In particular, increasing evidence indicates that inflammation contributes to susceptibility to depression, which is a leading cause of disability, and for which current treatments are often inadequate. We hypothesized that targeting Toll-like receptor 4 (TLR4), one of the main signaling pathways for triggering an inflammatory response, would lessen stress-induced depression-like behaviors in mice. TLR4 inhibition with the CNS-penetrating drug (+)-naloxone that is a TLR4 antagonist but is inactive at opiate receptors, reversed chronic restraint stress-induced impairments of various depression-like behaviors, as well as cognitive tests in male mice but had no effect in female mice. These effects might be mediated by interferon-β (IFNβ) pathway in microglial cells. Altogether, our results confirmed the critical role of TLR4 in mediating depressive-like behaviors and cognitive impairments and demonstrated that (+)-naloxone might be a promising therapeutic strategy for depression.

(+)-Naloxone blocks Toll-like receptor 4 to ameliorate deleterious effects of stress on male mouse behaviors

Depression is a leading cause of disability worldwide and current treatments are often inadequate for many patients. Increasing evidence indicates that inflammation contributes to susceptibility to depression. We hypothesized that targeting Toll-like receptor 4 (TLR4), one of the main signaling pathways for triggering an inflammatory response, would lessen stress-induced depression-like behaviors in male mice. TLR4 inhibition with the CNS-penetrating drug (+)-naloxone that is a TLR4 antagonist but is inactive at opiate receptors increased resistance to the learned helplessness model of depression and provided an antidepressant-like effect in the tail suspension test. (+)-Naloxone administration also reversed chronic restraint stress-induced impairments in social behavior and novel object recognition. These effects involved blockade of stress-induced activation of glycogen synthase kinase 3β (GSK3β), NF-κB, IFN regulatory factor 3 (IRF3) and nitric oxide production, and reduced levels of the cytokines tumor necrosis factor-α (TNFα) and interferon-β (IFNβ). These findings demonstrate that blocking TLR4 with (+)-naloxone effectively diminishes several detrimental responses to stress and raise the possibility that (+)-naloxone may be a feasible intervention for depression.

Toll-like receptor 2 (TLR2)-deficiency impairs male mouse recovery from a depression-like state

Major depression is a prevalent, debilitating disease, yet therapeutic interventions for depression are frequently inadequate. Many clinical and pre-clinical studies have demonstrated that depression is associated with aberrant activation of the inflammatory system, raising the possibility that reducing inflammation may provide antidepressant effects. Using the learned helplessness mouse model, we tested if susceptibility or recovery were affected by deficiency in either of two receptors that initiate inflammatory signaling, Toll-like receptor-4 (TLR4) and TLR2, using knockout male mice. TLR4^-/- mice displayed a strong resistance to learned helplessness, confirming that blocking inflammatory signaling through TLR4 provides robust protection against this depression-like behavior. Surprisingly, TLR2^-/- mice displayed increased susceptibility to learned helplessness, indicating that TLR2-mediated signaling counteracts susceptibility. TLR2-mediated signaling also promotes recovery, as TLR2^-/- mice demonstrated a severe impairment in recovery from learned helplessness. That TLR2 actually protects from learned helplessness was further verified by the finding that administration of the TLR2 agonist Pam3CSK4 reduced susceptibility to learned helplessness. Treatment with Pam3CSK4 also reversed chronic restraint stress-induced impaired sociability and impaired learning in the novel object recognition paradigm, demonstrating that TLR2 stimulation can protect from multiple impairments caused by stress. In summary, these results demonstrate that TLR2-mediated signaling provides a counter-signal to oppose deleterious effects of stress that may be related to depression, and indicate that TLR2 and TLR4 act oppositely to balance mood-relevant responses to stress.

Brain Penetrable Histone Deacetylase 6 Inhibitor SW-100 Ameliorates Memory and Learning Impairments in a Mouse Model of Fragile X Syndrome

Disease-modifying therapies are needed for Fragile X Syndrome (FXS), as at present there are no effective treatments or cures. Herein, we report on a tetrahydroquinoline-based selective histone deacetylase 6 (HDAC6) inhibitor SW-100, its pharmacological and ADMET properties, and its ability to improve upon memory performance in a mouse model of FXS, Fmr1^-/- mice. This small molecule demonstrates good brain penetrance, low-nanomolar potency for the inhibition of HDAC6 (IC₅₀ = 2.3 nM), with at least a thousand-fold selectivity over all other class I, II, and IV HDAC isoforms. Moreover, through its inhibition of the α-tubulin deacetylase domain of HDAC6 (CD2), in cells SW-100 upregulates α-tubulin acetylation with no effect on histone acetylation and selectively restores the impaired acetylated α-tubulin levels in the hippocampus of Fmr1^-/- mice. Lastly, SW-100 ameliorates several memory and learning impairments in Fmr1^-/- mice, thus modeling the intellectual deficiencies associated with FXS, and hence providing a strong rationale for pursuing HDAC6-based therapies for the treatment of this rare disease.

Distinct characteristics of hippocampal pathogenic TH17 cells in a mouse model of depression

Increasing evidence indicates that multiple actions of the immune system are closely intertwined with the development of depression and subsequent recovery processes. One of these interactions is substantial evidence that the TH17 subtype of CD4+ T cells promotes susceptibility to depression-like behaviors in mice. Comparing subtypes of CD4+ T cells, we found that administration of TH17 cells, but not TH1 cells or TREGS, promoted susceptibility to learned-helplessness depressive-like behavior and accumulated in the hippocampus of learned helpless mice. Adoptively transferred TH17 cells into Rag2-/- mice that are devoid of endogenous T cells increased susceptibility to learned helplessness, demonstrating that increased peripheral TH17 cells are capable of modulating depression-like behavior. Moreover, in wild-type mice, adoptively transferred TH17 cells accumulated in the hippocampus of learned-helpless mice and induced endogenous TH17 cell differentiation. Hippocampal TH17 cells from learned-helpless mice expressed markers of pathogenic TH17 cells (CCR6, IL-23R) and of follicular cells (CXCR5, PD-1), indicating that the hippocampal cells are TFH-17-like cells. Knockout of CCR6 blocked TH17 cells from promoting learned helplessness, which was associated with increased expression of PD-1 in CCR6-deficient TH17 cells. In summary, these results reinforce the conclusion that depression-like behaviors are selectively facilitated by TH17 cells, and revealed that these cells in the hippocampus of learned helpless mice display characteristics of TFH17-like cells, which may contribute to their pathogenic actions in promoting depression.

TNFα disrupts blood brain barrier integrity to maintain prolonged depressive-like behavior in mice

Recovery from major depressive disorder is difficult, particularly in patients who are refractory to antidepressant treatments. To examine factors that regulate recovery, we developed a prolonged learned helplessness depression model in mice. After the induction of learned helplessness, mice were separated into groups that recovered or did not recover within 4 weeks. Comparisons were made between groups in hippocampal proteins, inflammatory cytokines, and blood brain barrier (BBB) permeability. Compared with mice that recovered and control mice, non-recovered mice displaying prolonged learned helplessness had greater hippocampal activation of glycogen synthase kinase-3 (GSK3), higher levels of tumor necrosis factor-α (TNFα), interleukin-17A, and interleukin-23, increased permeability of the blood brain barrier (BBB), and lower levels of the BBB tight junction proteins occludin, ZO1, and claudin-5. Treatment with the GSK3 inhibitor TDZD-8 reduced inflammatory cytokine levels, increased tight junction protein levels, and reversed impaired recovery from learned helplessness, demonstrating that prolonged learned helplessness is reversible and is maintained by abnormally active GSK3. In non-recovered mice with prolonged learned helpless, stimulation of sphingosine 1-phosphate receptors by Fingolimod or administration of the TNFα inhibitor etanercept repaired the BBB and reversed impaired recovery from prolonged learned helplessness. Thus, disrupted BBB integrity mediated in part by TNFα contributes to blocking recovery from prolonged learned helplessness depression-like behavior. Overall, this report describes a new model of prolonged depression-like behavior and demonstrates that stress-induced GSK3 activation contributes to disruption of BBB integrity mediated by inflammation, particularly TNFα, which contributes to impaired recovery from prolonged learned helplessness.

Ketamine up-regulates a cluster of intronic miRNAs within the serotonin receptor 2C gene by inhibiting glycogen synthase kinase-3

OBJECTIVES

We examined mechanisms that contribute to the rapid antidepressant effect of ketamine in mice that is dependent on glycogen synthase kinase-3 (GSK3) inhibition.

METHODS

We measured serotonergic (5HT)-2C-receptor (5HTR2C) cluster microRNA (miRNA) levels in mouse hippocampus after administering an antidepressant dose of ketamine (10 mg/kg) in wild-type and GSK3 knockin mice, after GSK3 inhibition with L803-mts, and in learned helpless mice.

RESULTS

Ketamine up-regulated cluster miRNAs 448-3p, 764-5p, 1264-3p, 1298-5p and 1912-3p (2- to 11-fold). This up-regulation was abolished in GSK3 knockin mice that express mutant constitutively active GSK3. The GSK3 specific inhibitor L803-mts was antidepressant in the learned helplessness and novelty suppressed feeding depression-like behaviours and up-regulated the 5HTR2C miRNA cluster in mouse hippocampus. After administration of the learned helplessness paradigm mice were divided into cohorts that were resilient (non-depressed) or were susceptible (depressed) to learned helplessness. The resilient, but not depressed, mice displayed increased hippocampal levels of miRNAs 448-3p and 1264-3p. Administration of an antagonist to miRNA 448-3p diminished the antidepressant effect of ketamine in the learned helplessness paradigm, indicating that up-regulation of miRNA 448-3p provides an antidepressant action.

CONCLUSIONS

These findings identify a new outcome of GSK3 inhibition by ketamine that may contribute to antidepressant effects.

Intranasal siRNA administration reveals IGF2 deficiency contributes to impaired cognition in Fragile X syndrome mice

Molecular mechanisms underlying learning and memory remain imprecisely understood, and restorative interventions are lacking. We report that intranasal administration of siRNAs can be used to identify targets important in cognitive processes and to improve genetically impaired learning and memory. In mice modeling the intellectual deficiency of Fragile X syndrome, intranasally administered siRNA targeting glycogen synthase kinase-3β (GSK3β), histone deacetylase-1 (HDAC1), HDAC2, or HDAC3 diminished cognitive impairments. In WT mice, intranasally administered brain-derived neurotrophic factor (BDNF) siRNA or HDAC4 siRNA impaired learning and memory, which was partially due to reduced insulin-like growth factor-2 (IGF2) levels because the BDNF siRNA- or HDAC4 siRNA-induced cognitive impairments were ameliorated by intranasal IGF2 administration. In Fmr1^-/- mice, hippocampal IGF2 was deficient, and learning and memory impairments were ameliorated by IGF2 intranasal administration. Therefore intranasal siRNA administration is an effective means to identify mechanisms regulating cognition and to modulate therapeutic targets.

Stressed and Inflamed, Can GSK3 Be Blamed?

Psychological stress has a pervasive influence on our lives. In many cases adapting to stress strengthens organisms, but chronic or severe stress is usually harmful. One surprising outcome of psychological stress is the activation of an inflammatory response that resembles inflammation caused by infection or trauma. Excessive psychological stress and the consequential inflammation in the brain can increase susceptibility to psychiatric diseases, such as depression, and impair learning and memory, including in some patients with cognitive deficits. An emerging target to control detrimental outcomes of stress and inflammation is glycogen synthase kinase-3 (GSK3). GSK3 promotes inflammation, partly by regulating key transcription factors in the inflammation signaling pathway, and GSK3 can impair learning by promoting inflammation and by inhibiting long-term potentiation (LTP). Drugs inhibiting GSK3 may prove beneficial for controlling mood and cognitive impairments caused by excessive stress and the associated neuroinflammation.

Up-regulation of insulin-like growth factor 2 by ketamine requires glycogen synthase kinase-3 inhibition

An antidepressant dose of the rapidly-acting ketamine inhibits glycogen synthase kinase-3 (GSK3) in mouse hippocampus, and this inhibition is required for the antidepressant effect of ketamine in learned helplessness depression-like behavior. Here we report that treatment with an antidepressant dose of ketamine (10mg/kg) increased expression of insulin-like growth factor 2 (IGF2) in mouse hippocampus, an effect that required ketamine-induced inhibition of GSK3. Ketamine also inhibited hippocampal GSK3 and increased expression of hippocampal IGF2 in mice when administered after the induction of learned helplessness. Treatment with the specific GSK3 inhibitor L803-mts was sufficient to up-regulate hippocampal IGF2 expression. Administration of IGF2 siRNA reduced ketamine's antidepressant effect in the learned helplessness paradigm. Mice subjected to the learned helplessness paradigm were separated into two groups, those that were resilient (non-depressed) and those that were susceptible (depressed). Non-depressed resilient mice displayed higher expression of IGF2 than susceptible mice. These results indicate that IGF2 contributes to ketamine's antidepressant effect and that IGF2 may confer resilience to depression-like behavior.

Cotinine administration improves impaired cognition in the mouse model of Fragile X syndrome

Cotinine is the major metabolite of nicotine and has displayed some capacity for improving cognition in mouse models following chronic administration. We tested if acute cotinine treatment is capable of improving cognition in the mouse model of Fragile X syndrome, Fmr1^-/- knockout mice, and if this is related to inhibition by cotinine treatment of glycogen synthase kinase-3β (GSK3β), which is abnormally active in Fmr1^-/- mice. Acute cotinine treatment increased the inhibitory serine-phosphorylation of GSK3β and the activating phosphorylation of AKT, which can mediate serine-phosphorylation of GSK3β, in both wild-type and Fmr1^-/- mouse hippocampus. Acute cotinine treatment improved cognitive functions of Fmr1^-/- mice in coordinate and categorical spatial processing, novel object recognition, and temporal ordering. However, cotinine failed to restore impaired cognition in GSK3β knockin mice, in which a serine9-to-alanine9 mutation blocks the inhibitory serine phosphorylation of GSK3β, causing GSK3β to be hyperactive. These results indicate that acute cotinine treatment effectively repairs impairments of these four cognitive tasks in Fmr1^-/- mice, and suggest that this cognition-enhancing effect of cotinine is linked to its induction of inhibitory serine-phosphorylation of GSK3. Taken together, these results show that nicotinic receptor agonists can act as cognitive enhancers in a mouse model of Fragile X syndrome and highlight the potential role of inhibiting GSK3β in mediating the beneficial effects of cotinine on memory.

Ketamine-induced inhibition of glycogen synthase kinase-3 contributes to the augmentation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor signaling

OBJECTIVES

Sub-anesthetic doses of ketamine have been found to provide rapid antidepressant actions, indicating that the cellular signaling systems targeted by ketamine are potential sites for therapeutic intervention. Ketamine acts as an antagonist of N-methyl-D-aspartate (NMDA) receptors, and animal studies indicate that subsequent augmentation of signaling by α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors is critical for the antidepressant outcome.

METHODS

In this study, we tested if the inhibitory effect of ketamine on glycogen synthase kinase-3 (GSK3) affected hippocampal cell-surface AMPA receptors using immunoblotting of membrane and synaptosomal extracts from wild-type and GSK3 knockin mice.

RESULTS

Treatment with an antidepressant dose of ketamine increased the hippocampal membrane level of the AMPA glutamate receptor (GluA)1 subunit, but did not alter the localization of GluA2, GluA3, or GluA4. This effect of ketamine was abrogated in GSK3 knockin mice expressing mutant GSK3 that cannot be inhibited by ketamine, demonstrating that ketamine-induced inhibition of GSK3 is necessary for up-regulation of cell surface AMPA GluA1 subunits. AMPA receptor trafficking is regulated by post-synaptic density-95 (PSD-95), a substrate for GSK3. Ketamine treatment decreased the hippocampal membrane level of phosphorylated PSD-95 on Thr-19, the target of GSK3 that promotes AMPA receptor internalization.

CONCLUSIONS

These results demonstrate that ketamine-induced inhibition of GSK3 causes reduced phosphorylation of PSD-95, diminishing the internalization of AMPA GluA1 subunits to allow for augmented signaling through AMPA receptors following ketamine treatment.

GSK3β isoform-selective regulation of depression, memory and hippocampal cell proliferation

Abnormally active glycogen synthase kinase-3 (GSK3) contributes to pathological processes in multiple psychiatric and neurological disorders. Modeled in mice, this includes increasing susceptibility to dysregulation of mood-relevant behaviors, impairing performance in several cognitive tasks and impairing adult hippocampal neural precursor cell (NPC) proliferation. These deficits are all evident in GSK3α/β knockin mice, in which serine-to-alanine mutations block the inhibitory serine phosphorylation regulation of both GSK3 isoforms, leaving GSK3 hyperactive. It was unknown if both GSK3 isoforms perform redundant actions in these processes, or if hyperactivity of one GSK3 isoform has a predominant effect. To test this, we examined GSK3α or GSK3β knockin mice in which only one isoform was mutated to a hyperactive form. Only GSK3β, not GSK3α, knockin mice displayed heightened vulnerability to the learned helplessness model of depression-like behavior. Three cognitive measures impaired in GSK3α/β knockin mice showed differential regulation by GSK3 isoforms. Novel object recognition was impaired in GSK3β, not in GSK3α, knockin mice, whereas temporal order memory was not impaired in GSK3α or GSK3β knockin mice, and co-ordinate spatial processing was impaired in both GSK3α and GSK3β knockin mice. Adult hippocampal NPC proliferation was severely impaired in GSK3β knockin mice, but not impaired in GSK3α knockin mice. Increased activity of GSK3β, in the absence of overexpression or disease pathology, is sufficient to impair mood regulation, novel object recognition and hippocampal NPC proliferation, whereas hyperactive GSK3α individually does not impair these processes. These results show that hyperactivity of the two GSK3 isoforms execute non-redundant effects on these processes.

Lithium to the Rescue

Lithium, an element that Mother Nature has put in some drinking water sources, has been used for its curative powers for centuries. Today, it's given in capsule form as a mood stabilizer for bipolar disorder and depression. New research, however, reveals its role as a neuroprotector, and suggests that a better understanding of the role enzymes modulated by lithium play could lead to new treatments for Alzheimer's disease, Parkinson's disease, multiple sclerosis, and other neurodegenerative disorders.

A pre-conditioning stress accelerates increases in mouse plasma inflammatory cytokines induced by stress

Background

Major depressive disorder is a prevalent disease that is inadequately treated with currently available interventions. Stress increases susceptibility to depression in patients and rodent models. Depression is also associated with aberrant activation of inflammation, such as increases in circulating levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNFα). The two main goals of this study were (i) to identify cytokine changes measuring a broad panel of 19 cytokines, and (ii) to test if a pre-conditioning stress altered the inflammatory response to a subsequent stress.

Result

Stress-induced changes in mouse plasma cytokines were measured by multiplex following administration of one or two daily stresses of inescapable foot shocks using the learned helplessness paradigm for modeling depression-like behavior.

Administration of inescapable foot shocks increased plasma levels of IL-1β, IL-6, TNFα, IL-3, IL-10, IL-13, IL-17A, IL-5, GM-CSF, IL-12(p70), IFN-γ, MIP-1α, MIP-1β, IL-1α, IL-2, KC, RANTES and G-CSF, with peak levels occurring in the range of 6 to 12 hr after stress. Pre-conditioning the mice 24 hr before with an equivalent inescapable foot shock stress resulted in similar magnitudes of increases in most cytokines as occurred after a single stress, but accelerated the increase, causing the levels of most cytokines to peak 1 hr after stress. These results demonstrate that a single stress induces the expression of many cytokines, and that sequential, daily stresses accelerates the rate of cytokine production.

Conclusions

Acute stress broadly activates inflammation in mice, and the inflammatory response is more rapid following repeated stress, actions that may contribute to deleterious effects of stress on depression and other stress-linked diseases.

Impairments in cognition and neural precursor cell proliferation in mice expressing constitutively active glycogen synthase kinase-3

Brain glycogen synthase kinase-3 (GSK3) is hyperactive in several neurological conditions that involve impairments in both cognition and neurogenesis. This raises the hypotheses that hyperactive GSK3 may directly contribute to impaired cognition, and that this may be related to deficiencies in neural precursor cells (NPC). To study the effects of hyperactive GSK3 in the absence of disease influences, we compared adult hippocampal NPC proliferation and performance in three cognitive tasks in male and female wild-type (WT) mice and GSK3 knockin mice, which express constitutively active GSK3. NPC proliferation was ~40% deficient in both male and female GSK3 knockin mice compared with WT mice. Environmental enrichment (EE) increased NPC proliferation in male, but not female, GSK3 knockin mice and WT mice. Male and female GSK3 knockin mice exhibited impairments in novel object recognition, temporal order memory, and coordinate spatial processing compared with gender-matched WT mice. EE restored impaired novel object recognition and temporal ordering in both sexes of GSK3 knockin mice, indicating that this repair was not dependent on NPC proliferation, which was not increased by EE in female GSK3 knockin mice. Acute 1 h pretreatment with the GSK3 inhibitor TDZD-8 also improved novel object recognition and temporal ordering in male and female GSK3 knockin mice. These findings demonstrate that hyperactive GSK3 is sufficient to impair adult hippocampal NPC proliferation and to impair performance in three cognitive tasks in both male and female mice, but these changes in NPC proliferation do not directly regulate novel object recognition and temporal ordering tasks.

Inflammation and lithium: clues to mechanisms contributing to suicide-linked traits

Suicide is one of the leading causes of death in the United States, yet it remains difficult to understand the mechanistic provocations and to intervene therapeutically. Stress is recognized as a frequent precursor to suicide. Psychological stress is well established to cause activation of the inflammatory response, including causing neuroinflammation, an increase of inflammatory molecules in the central nervous system (CNS). Neuroinflammation is increasingly recognized as affecting many aspects of CNS functions and behaviors. In particular, much evidence demonstrates that inflammatory markers are elevated in traits that have been linked to suicidal behavior, including aggression, impulsivity and depression. Lithium is recognized as significantly reducing suicidal behavior, is anti-inflammatory and diminishes aggression, impulsivity and depression traits, each of which is associated with elevated inflammation. The anti-inflammatory effects of lithium result from its inhibition of glycogen synthase kinase-3 (GSK3). GSK3 has been demonstrated to strongly promote inflammation, aggressive behavior in rodents and depression-like behaviors in rodents, whereas regulation of impulsivity by GSK3 has not yet been investigated. Altogether, evidence is building supporting the hypothesis that stress activates GSK3, which in turn promotes inflammation, and that inflammation is linked to behaviors associated with suicide, including particularly aggression, impulsivity and depression. Further investigation of these links may provide a clearer understanding of the causes of suicidal behavior and provide leads for the development of effective preventative interventions, which may include inhibitors of GSK3.

Glycogen synthase kinase-3 (GSK3): regulation, actions, and diseases

Glycogen synthase kinase-3 (GSK3) may be the busiest kinase in most cells, with over 100 known substrates to deal with. How does GSK3 maintain control to selectively phosphorylate each substrate, and why was it evolutionarily favorable for GSK3 to assume such a large responsibility? GSK3 must be particularly adaptable for incorporating new substrates into its repertoire, and we discuss the distinct properties of GSK3 that may contribute to its capacity to fulfill its roles in multiple signaling pathways. The mechanisms regulating GSK3 (predominantly post-translational modifications, substrate priming, cellular trafficking, protein complexes) have been reviewed previously, so here we focus on newly identified complexities in these mechanisms, how each of these regulatory mechanism contributes to the ability of GSK3 to select which substrates to phosphorylate, and how these mechanisms may have contributed to its adaptability as new substrates evolved. The current understanding of the mechanisms regulating GSK3 is reviewed, as are emerging topics in the actions of GSK3, particularly its interactions with receptors and receptor-coupled signal transduction events, and differential actions and regulation of the two GSK3 isoforms, GSK3α and GSK3β. Another remarkable characteristic of GSK3 is its involvement in many prevalent disorders, including psychiatric and neurological diseases, inflammatory diseases, cancer, and others. We address the feasibility of targeting GSK3 therapeutically, and provide an update of its involvement in the etiology and treatment of several disorders.

Glycogen synthase kinase-3 inhibitors reverse deficits in long-term potentiation and cognition in fragile X mice

BACKGROUND

Identifying feasible therapeutic interventions is crucial for ameliorating the intellectual disability and other afflictions of fragile X syndrome (FXS), the most common inherited cause of intellectual disability and autism. Hippocampal glycogen synthase kinase-3 (GSK3) is hyperactive in the mouse model of FXS (FX mice), and hyperactive GSK3 promotes locomotor hyperactivity and audiogenic seizure susceptibility in FX mice, raising the possibility that specific GSK3 inhibitors may improve cognitive processes.

METHODS

We tested if specific GSK3 inhibitors improve deficits in N-methyl-D-aspartate receptor-dependent long-term potentiation at medial perforant path synapses onto dentate granule cells and dentate gyrus-dependent cognitive behavioral tasks.

RESULTS

GSK3 inhibitors completely rescued deficits in long-term potentiation at medial perforant path-dentate granule cells synapses in FX mice. Furthermore, synaptosomes from the dentate gyrus of FX mice displayed decreased inhibitory serine-phosphorylation of GSK3β compared with wild-type littermates. The potential therapeutic utility of GSK3 inhibitors was further tested on dentate gyrus-dependent cognitive behaviors. In vivo administration of GSK3 inhibitors completely reversed impairments in several cognitive tasks in FX mice, including novel object detection, coordinate and categorical spatial processing, and temporal ordering for visual objects.

CONCLUSIONS

These findings establish that synaptic plasticity and cognitive deficits in FX mice can be improved by intervention with inhibitors of GSK3, which may prove therapeutically beneficial in FXS.

Astrocytes modulate the polarization of CD4+ T cells to Th1 cells

T-cell characteristics are dynamic and influenced by multiple factors. To test whether cells and the environment in the central nervous system (CNS) can influence T-cells, we tested if culturing mouse CD4⁺ T-cells on mouse primary astrocytes, compared with standard feeder cells, modified T-cell polarization to Th1 and Treg subtypes. Astrocytes supported the production of Th1 cells and Tregs, which was diminished by inflammatory activation of astrocytes, and glutamate accumulation that may result from impaired glutamate uptake by astrocytes strongly promoted Th1 production. These results demonstrate that astrocytes and the environment in the CNS have the capacity to regulate T-cell characteristics.

Glycogen synthase kinase-3 inhibitors: Rescuers of cognitive impairments

Impairment of cognitive processes is a devastating outcome of many diseases, injuries, and drugs affecting the central nervous system (CNS). Most often, very little can be done by available therapeutic interventions to improve cognitive functions. Here we review evidence that inhibition of glycogen synthase kinase-3 (GSK3) ameliorates cognitive deficits in a wide variety of animal models of CNS diseases, including Alzheimer's disease, Fragile X syndrome, Down syndrome, Parkinson's disease, spinocerebellar ataxia type 1, traumatic brain injury, and others. GSK3 inhibitors also improve cognition following impairments caused by therapeutic interventions, such as cranial irradiation for brain tumors. These findings demonstrate that GSK3 inhibitors are able to ameliorate cognitive impairments caused by a diverse array of diseases, injury, and treatments. The improvements in impaired cognition instilled by administration of GSK3 inhibitors appear to involve a variety of different mechanisms, such as supporting long-term potentiation and diminishing long-term depression, promotion of neurogenesis, reduction of inflammation, and increasing a number of neuroprotective mechanisms. The potential for GSK3 inhibitors to repair cognitive deficits associated with many conditions warrants further investigation of their potential for therapeutic interventions, particularly considering the current dearth of treatments available to reduce loss of cognitive functions.

Lithium treatment alleviates impaired cognition in a mouse model of fragile X syndrome

Fragile X syndrome (FXS) is caused by suppressed expression of fragile X mental retardation protein (FMRP), which results in intellectual disability accompanied by many variably manifested characteristics, such as hyperactivity, seizures and autistic-like behaviors. Treatment of mice that lack FMRP, Fmr1 knockout (KO) mice, with lithium has been reported to ameliorate locomotor hyperactivity, prevent hypersensitivity to audiogenic seizures, improve passive avoidance behavior and attenuate sociability deficits. To focus on the defining characteristic of FXS, which is cognitive impairment, we tested if lithium treatment ameliorated impairments in four cognitive tasks in Fmr1 KO mice, tested if the response to lithium differed in adolescent and adult mice and tested if therapeutic effects persisted after discontinuation of lithium administration. Fmr1 KO mice displayed impaired cognition in the novel object detection task, temporal ordering for objects task and coordinate and categorical spatial processing tasks. Chronic lithium treatment of adolescent (from 4 to 8 weeks of age) and adult (from 8 to 12 weeks of age) mice abolished cognitive impairments in all four cognitive tasks. Cognitive deficits returned after lithium treatment was discontinued for 4 weeks. These results show that Fmr1 KO mice exhibit severe impairments in these cognitive tasks, that lithium is equally effective in normalizing cognition in these tasks whether it is administered to young or adult mice and that lithium administration must be continued for the cognitive improvements to be sustained. These findings provide further evidence that lithium administration may be beneficial for individuals with FXS.

Regulation of Th1 cells and experimental autoimmune encephalomyelitis by glycogen synthase kinase-3

Experimental autoimmune encephalomyelitis (EAE) is a rodent model of multiple sclerosis (MS), a debilitating autoimmune disease of the CNS, for which only limited therapeutic interventions are available. Because MS is mediated in part by autoreactive T cells, particularly Th17 and Th1 cells, in the current study, we tested whether inhibitors of glycogen synthase kinase-3 (GSK3), previously reported to reduce Th17 cell generation, also alter Th1 cell production or alleviate EAE. GSK3 inhibitors were found to impede the production of Th1 cells by reducing STAT1 activation. Molecularly reducing the expression of either of the two GSK3 isoforms demonstrated that Th17 cell production was sensitive to reduced levels of GSK3β and Th1 cell production was inhibited in GSK3α-deficient cells. Administration of the selective GSK3 inhibitors TDZD-8, VP2.51, VP0.7, or L803-mts significantly reduced the clinical symptoms of myelin oligodendrocyte glycoprotein35-55-induced EAE in mice, nearly eliminating the chronic progressive phase, and reduced the number of Th17 and Th1 cells in the spinal cord. Administration of TDZD-8 or L803-mts after the initial disease episode alleviated clinical symptoms in a relapsing-remitting model of proteolipid protein139-151-induced EAE. Furthermore, deletion of GSK3β specifically in T cells was sufficient to alleviate myelin oligodendrocyte glycoprotein35-55-induced EAE. These results demonstrate the isoform-selective effects of GSK3 on T cell generation and the therapeutic effects of GSK3 inhibitors in EAE, as well as showing that GSK3 inhibition in T cells is sufficient to reduce the severity of EAE, suggesting that GSK3 may be a feasible target for developing new therapeutic interventions for MS.

Inflammatory T helper 17 cells promote depression-like behavior in mice

BACKGROUND

Recognition of substantial immune-neural interactions is revising dogmas about their insular actions and revealing that immune-neural interactions can substantially impact central nervous system functions. The inflammatory cytokine interleukin-6 promotes susceptibility to depression and drives production of inflammatory T helper 17 (Th17) T cells, raising the hypothesis that in mouse models, Th17 cells promote susceptibility to depression-like behaviors.

METHODS

Behavioral characteristics were measured in male mice administered Th17 cells, CD4(+) cells, or vehicle and in retinoid-related orphan receptor-γT (RORγT)(+/GFP) mice or male mice treated with RORγT inhibitor or anti-interleukin-17A antibodies.

RESULTS

Mouse brain Th17 cells were elevated by learned helplessness and chronic restraint stress, two common depression-like models. Th17 cell administration promoted learned helplessness in 89% of mice in a paradigm where no vehicle-treated mice developed learned helplessness, and impaired novelty suppressed feeding and social interaction behaviors. Mice deficient in the RORγT transcription factor necessary for Th17 cell production exhibited resistance to learned helplessness, identifying modulation of RORγT as a potential intervention. Treatment with the RORγT inhibitor SR1001, or anti-interleukin-17A antibodies to abrogate Th17 cell function, reduced Th17-dependent learned helplessness.

CONCLUSIONS

These findings indicate that Th17 cells are increased in the brain during depression-like states, promote depression-like behaviors in mice, and specifically inhibiting the production or function of Th17 cells reduces vulnerability to depression-like behavior, suggesting antidepressant effects may be attained by targeting Th17 cells.

Impaired translocation and activation of mitochondrial Akt1 mitigated mitochondrial oxidative phosphorylation Complex V activity in diabetic myocardium

Insulin can translocate Akt to mitochondria in cardiac muscle. The goals of this study were to define sub-mitochondrial localization of the translocated Akt, to dissect the effects of insulin on Akt isoform translocation, and to determine the direct effect of mitochondrial Akt activation on Complex V activity in normal and diabetic myocardium. The translocated Akt sequentially localized to the mitochondrial intermembrane space, inner membrane, and matrix. To confirm Akt translocation, in vitro import assay showed rapid entry of Akt into mitochondria. Akt isoforms were differentially regulated by insulin stimulation, only Akt1 translocated into mitochondria. In the insulin-resistant Type 2 diabetes model, Akt1 translocation was blunted. Mitochondrial activation of Akt1 increased Complex V activity by 24% in normal myocardium in vivo and restored Complex V activity in diabetic myocardium. Basal mitochondrial Complex V activity was lower by 22% in the Akt1(-/-) myocardium. Insulin-stimulated Complex V activity was not impaired in the Akt1(-/-) myocardium, due to compensatory translocation of Akt2 to mitochondria. Akt1 is the primary isoform that relayed insulin signaling to mitochondria and modulated mitochondrial Complex V activity. Activation of mitochondrial Akt1 enhanced ATP production and increased phosphocreatine in cardiac muscle cells. Dysregulation of this signal pathway might impair mitochondrial bioenergetics in diabetic myocardium.

DDX3 regulates DNA damage-induced apoptosis and p53 stabilization

The DEAD box protein family member DDX3 was previously identified as an inhibitor of death receptor-mediated extrinsic apoptotic signaling. However, there had been no studies of the role of DDX3 in regulating the other major type of apoptosis, intrinsic apoptotic signaling, which was examined here. Intrinsic apoptosis was induced in MCF-7 cells by treatment with staurosporine, a general kinase inhibitor, thapsigargin, which induces endoplasmic reticulum (ER) stress, and camptothecin, which causes DNA damage. Each of these treatments caused time-dependent activation of caspase-7, the predominant executioner caspase in these cells. Depletion of DDX3 using shRNA did not alter apoptotic responses to staurosporine or thapsigargin. However, caspase-7 activation induced by camptothecin was regulated by DDX3 in a manner dependent on the functional status of p53. Depletion of DDX3 abrogated camptothecin-induced caspase-7 activation in MCF-7 cells expressing functional wild-type p53, but oppositely potentiated camptothecin-mediated caspase activation in cells expressing mutant or non-functional p53, which was accompanied by increased activation of the extrinsic apoptotic signaling initiator caspase-8. In MCF-7 cells, depletion of DDX3 reduced by more than 50% camptothecin-induced p53 accumulation, and this effect was blocked by inhibition of the proteasome with MG132, indicating that DDX3 regulates p53 not at expression level but rather its stabilization after DNA damage. Co-immunoprecipitation experiments demonstrated that DDX3 associates with p53, and overexpression of DDX3 was sufficient to double the accumulation of p53 in the nucleus after DNA damage. Thus, DDX3 associates with p53, increases p53 accumulation, and positively regulates camptothecin-induced apoptotic signaling in cells expressing functional wild-type p53, whereas in cells expressing mutant or non-functional p53 DDX3 inhibits activation of the extrinsic apoptotic pathway to reduce caspase activation. These results demonstrate that DDX3 not only regulates extrinsic apoptotic signaling, as previously reported, but also selectively regulates intrinsic apoptotic signaling following DNA damage.

Glycogen synthase kinase-3 levels and phosphorylation undergo large fluctuations in mouse brain during development

OBJECTIVES

Dysregulated glycogen synthase kinase-3 (GSK3) may contribute to the pathophysiology of mood disorders and other diseases, and appears to be a target of certain therapeutic drugs. The growing recognition of heightened vulnerability during development to many psychiatric diseases, including mood disorders, led us to test if there are developmental changes in mouse brain GSK3 and its regulation by phosphorylation and by therapeutic drugs.

METHODS

GSK3 levels and phosphorylation were measured at seven ages of development in the mouse cerebral cortex and hippocampus.

RESULTS

Two periods of rapid transitions in GSK3 levels were identified: a large rise between postnatal days 1 and 2 and three weeks of age, where GSK3 levels were as much as fourfold higher than adult mouse brain levels, and a rapid decline between 2-4 and eight weeks of age, when adult levels were reached. Inhibitory serine-phosphorylation of GSK3, particularly GSK3β, was extremely high in the one-day postnatal mouse brain, and rapidly declined thereafter. These developmental changes in GSK3 were equivalent in the male and female cerebral cortex, and differed from other signaling kinases, including Akt, extracellular-regulated kinases 1/2, c-Jun N-terminal kinase, and p38 levels and phosphorylation. In contrast to the adult mouse brain, where administration of lithium or fluoxetine rapidly and robustly increased serine-phosphorylation of GSK3, in young mice these responses were blunted or absent.

CONCLUSIONS

High brain levels of GSK3 and large fluctuations in its levels and phosphorylation in the juvenile and adolescent mouse brain raise the possibility that they may contribute to destabilized mood regulation induced by environmental and genetic factors.

Disruption of circadian rhythmicity and suprachiasmatic action potential frequency in a mouse model with constitutive activation of glycogen synthase kinase 3

Glycogen synthase kinase 3 (GSK3) is a serine/threonine kinase that has been implicated in psychiatric diseases, neurodevelopment, and circadian regulation. Both GSK3 isoforms, α and β, exhibit a 24-h variation of inhibitory phosphorylation within the suprachiasmatic nucleus (SCN), the primary circadian pacemaker. We examined the hypothesis that rhythmic GSK3 activity is critical for robust circadian rhythmicity using GSK3α(21A/21A)/β(9A/9A) knock-in mice with serine-alanine substitutions at the inhibitory phosphorylation sites, making both forms constitutively active. We monitored wheel-running locomotor activity of GSK3 knock-in mice and used loose-patch electrophysiology to examine the effect of chronic GSK3 activity on circadian behavior and SCN neuronal activity. Double transgenic GSK3α/β knock-in mice exhibit disrupted behavioral rhythmicity, including significantly decreased rhythmic amplitude, lengthened active period, and increased activity bouts per day. This behavioral disruption was dependent on chronic activation of both GSK3 isoforms and was not seen in single transgenic GSK3α or GSK3β knock-in mice. Underlying the behavioral changes, SCN neurons from double transgenic GSK3α/β knock-in mice exhibited significantly higher spike rates during the subjective night compared to those from wild-type controls, with no differences detected during the subjective day. These results suggest that constitutive activation of GSK3 results in the loss of the typical day/night variation of SCN neuronal activity. Together, these results implicate GSK3 activity as a critical regulator of circadian behavior and neurophysiological rhythms. Because GSK3 has been implicated in numerous pathologies, understanding how GSK3 modulates circadian rhythms and neurophysiological activity may lead to novel therapeutics for pathological disorders and circadian rhythm dysfunction.

Activation of the ATM-Snail pathway promotes breast cancer metastasis

The DNA damage response (DDR) is critical for the maintenance of genetic stability and serves as an anti-cancer barrier during early tumorigenesis. However, the role of the DDR in tumor progression and metastasis is less known. Here, we demonstrate that the ATM kinase, one of the critical DDR elements, is hyperactive in late stage breast tumor tissues with lymph-node metastasis and this hyperactivity correlates with elevated expression of the epithelial-mesenchymal transition marker, Snail. At the molecular level, we demonstrate that ATM regulates Snail stabilization by phosphorylation on Serine-100. Using mass spectrometry, we identified HSP90 as a critical binding protein of Snail in response to DNA damage. HSP90 binds to and stabilizes phosphorylated Snail. We further provide in vitro and in vivo evidence that activation of ATM-mediated Snail phosphorylation promotes tumor invasion and metastasis. Finally, we demonstrate that Snail Serine-100 phosphorylation is elevated in breast cancer tissues with lymph-node metastasis, indicating clinical significance of the ATM-Snail pathway. Together, our findings provide strong evidence that the ATM-Snail pathway promotes tumor metastasis, highlighting a previously undescribed role of the DDR in tumor invasion and metastasis.

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.

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.

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.

Regulation of cell survival mechanisms in Alzheimer's disease by glycogen synthase kinase-3

A pivotal role has emerged for glycogen synthase kinase-3 (GSK3) as an important contributor to Alzheimer's disease pathology. Evidence for the involvement of GSK3 in Alzheimer's disease pathology and neuronal loss comes from studies of GSK3 overexpression, GSK3 localization studies, multiple relationships between GSK3 and amyloid β-peptide (Aβ), interactions between GSK3 and the microtubule-associated tau protein, and GSK3-mediated apoptotic cell death. Apoptotic signaling proceeds by either an intrinsic pathway or an extrinsic pathway. GSK3 is well established to promote intrinsic apoptotic signaling induced by many insults, several of which may contribute to neuronal loss in Alzheimer's disease. Particularly important is evidence that GSK3 promotes intrinsic apoptotic signaling induced by Aβ. GSK3 appears to promote intrinsic apoptotic signaling by modulating proteins in the apoptosis signaling pathway and by modulating transcription factors that regulate the expression of proteins involved in apoptosis. Thus, GSK3 appears to contribute to several neuropathological mechanisms in Alzheimer's disease, including apoptosis-mediated neuronal loss.

Convergence of the mammalian target of rapamycin complex 1- and glycogen synthase kinase 3-β-signaling pathways regulates the innate inflammatory response

The PI3K pathway and its regulation of mammalian target of rapamycin complex 1 (mTORC1) and glycogen synthase kinase 3 (GSK3) play pivotal roles in controlling inflammation. In this article, we show that mTORC1 and GSK3-β converge and that the capacity of mTORC1 to affect the inflammatory response is due to the inactivation of GSK3-β. Inhibition of mTORC1 attenuated GSK3 phosphorylation and increased its kinase activity. Immunoprecipitation and in vitro kinase assays demonstrated that GSK3-β associated with a downstream target of mTORC1, p85S6K, and phosphorylated GSK3-β. Inhibition of S6K1 abrogated the phosphorylation of GSK3-β while increasing and decreasing the levels of IL-12 and IL-10, respectively, in LPS-stimulated monocytes. In contrast, the direct inhibition of GSK3 attenuated the capacity of S6K1 inhibition to influence the levels of IL-10 and IL-12 produced by LPS-stimulated cells. At the transcriptional level, mTORC1 inhibition reduced the DNA binding of CREB and this effect was reversed by GSK3 inhibition. As a result, mTORC1 inhibition increased the levels of NF-κB p65 associated with CREB-binding protein. Inhibition of NF-κB p65 attenuated rapamycin's ability to influence the levels of pro- or anti-inflammatory cytokine production in monocytes stimulated with LPS. These studies identify the molecular mechanism by which mTORC1 affects GSK3 and show that mTORC1 inhibition regulates pro- and anti-inflammatory cytokine production via its capacity to inactivate GSK3.

Glycogen synthase kinase-3 regulates endoplasmic reticulum (ER) stress-induced CHOP expression in neuronal cells

Endoplasmic reticulum (ER) stress, often resulting from cellular accumulation of misfolded proteins, occurs in many neurodegenerative disorders, in part because of the relatively long lifetime of neurons. Excessive accumulation of misfolded proteins activates the unfolded protein response (UPR) that dampens protein synthesis and promotes removal of misfolded proteins to support survival of ER-stressed cells. However, the UPR also initiates apoptotic signaling to kill cells if recovery is not achieved. Thus, there is much interest in identifying determinants of the life-death switch and interventions that promote recovery and survival. One intervention that has consistently been shown to protect cells from ER stress-induced apoptosis is application of inhibitors of glycogen synthase kinase-3 (GSK3). Therefore, we examined where in the UPR pathway GSK3 inhibitors intercede to impede signaling towards apoptosis. Apoptosis following UPR activation can be mediated by activation of two transcription factors, ATF4 and ATF6, that activate expression of the death-inducing transcription factor C/EBP homologous protein (CHOP/GADD153) following ER stress. We found that ER stress activated ATF6 and ATF4, but these responses were not inhibited by pretreatment with GSK3 inhibitors. However, inhibition of GSK3 effectively reduced the expression of CHOP, and this was apparent in several types of neural-related cells and was evident after application of several structurally diverse GSK3 inhibitors. Therefore, reduction of CHOP activation provides one mechanism by which inhibitors of GSK3 are capable of shifting cell fate towards survival instead of apoptosis following ER stress.

Glycogen synthase kinase-3 is an early determinant in the differentiation of pathogenic Th17 cells

CD4(+) T cells are critical for host defense but are also major drivers of immune-mediated diseases. The classical view of Th1 and Th2 subtypes of CD4(+) T cells was recently revised by the identification of the Th17 lineage of CD4(+) T cells that produce IL-17, which have been found to be critical in the pathogenesis of autoimmune and other diseases. Mechanisms controlling the differentiation of Th17 cells have been well described, but few feasible targets for therapeutically reducing Th17 cells are known. The generation of Th17 cells requires IL-6 and activation of STAT3. During polarization of CD4(+) T cells to Th17 cells, we found that inhibition of glycogen synthase kinase-3 (GSK3) blocked IL-6 production, STAT3 activation, and polarization to Th17 cells. Polarization of CD4(+) T cells to Th17 cells increased by 10-fold the expression of GSK3β protein levels in Th17 cells, whereas GSK3β was unaltered in regulatory T cells. Diminishing GSK3 activity either pharmacologically or molecularly blocked Th17 cell production, and increasing GSK3 activity promoted polarization to Th17 cells. In vivo inhibition of GSK3 in mice depleted constitutive Th17 cells in intestinal mucosa, blocked Th17 cell generation in the lung after Francisella tularensis infection, and inhibited the increase in spinal cord Th17 cells and disease symptoms in the experimental autoimmune encephalomyelitis mouse model of multiple sclerosis. These findings identify GSK3 as a critical mediator of Th17 cell production and indicate that GSK3 inhibitors provide a potential therapeutic intervention to control Th17-mediated diseases.

Evidence of reactive astrocytes but not peripheral immune system activation in a mouse model of Fragile X syndrome

Fragile X syndrome (FXS) is the most common form of inherited mental retardation and is one of the few known genetic causes of autism. FXS results from the loss of Fmr1 gene function; thus, Fmr1 knockout mice provide a model to study impairments associated with FXS and autism and to test potential therapeutic interventions. The inhibitory serine phosphorylation of glycogen synthase kinase-3 (GSK3) is lower in brain regions of Fmr1 knockout mice than wild-type mice and the GSK3 inhibitor lithium rescues several behavioral impairments in Fmr1 knockout mice. Therefore, we examined if the serine phosphorylation of GSK3 in Fmr1 knockout mice also was altered outside the brain and if administration of lithium ameliorated the macroorchidism phenotype. Additionally, since GSK3 regulates numerous functions of the immune system and immune alterations have been associated with autism, we tested if immune function is altered in Fmr1 knockout mice. The inhibitory serine phosphorylation of GSK3 was significantly lower in the testis and liver of Fmr1 knockout mice than wild-type mice, and chronic lithium treatment reduced macroorchidism in Fmr1 knockout mice. No alterations in peripheral immune function were identified in Fmr1 knockout mice. However, examination of glia, the immune cells of the brain, revealed reactive astrocytes in several brain regions of Fmr1 knockout mice and treatment with lithium reduced this in the striatum and cerebellum. These results provide further evidence of the involvement of dysregulated GSK3 in FXS, and demonstrate that lithium administration reduces macroorchidism and reactive astrocytes in Fmr1 knockout mice.

Glycogen synthase kinase-3 regulates inflammatory tolerance in astrocytes

Inflammatory tolerance is the down-regulation of inflammation upon repeated stimuli, which is well-established to occur in peripheral immune cells. However, less is known about inflammatory tolerance in the brain although it may provide an important protective mechanism from detrimental consequences of prolonged inflammation, which appears to occur in many psychiatric and neurodegenerative conditions. Array analysis of 308 inflammatory molecules produced by mouse primary astrocytes after two sequential stimulations with lipopolysaccharide (LPS) distinguished three classes, tolerant, sensitized and unaltered groups. For many of these inflammatory molecules, inhibition of glycogen synthase kinase-3 (GSK3) increased tolerance and reduced sensitization. Focusing on LPS-tolerance in interleukin-6 (IL-6) production, we found that microglia exhibited a strong tolerance response that matched that of macrophages, whereas astrocytes exhibited only partial tolerance. The astrocyte semi-tolerance was found to be regulated by GSK3. GSK3 inhibitors or knocking down GSK3 levels promoted LPS-tolerance and astrocytes expressing constitutively active GSK3 did not develop LPS-tolerance. These findings identify the critical role of GSK3 in counteracting IL-6 inflammatory tolerance in cells of the CNS, supporting the therapeutic potential of GSK3 inhibitors to reduce neuroinflammation by promoting tolerance.

GSK3 influences social preference and anxiety-related behaviors during social interaction in a mouse model of fragile X syndrome and autism

BACKGROUND

Nearly 1% of children in the United States exhibit autism spectrum disorders, but causes and treatments remain to be identified. Mice with deletion of the fragile X mental retardation 1 (Fmr1) gene are used to model autism because loss of Fmr1 gene function causes Fragile X Syndrome (FXS) and many people with FXS exhibit autistic-like behaviors. Glycogen synthase kinase-3 (GSK3) is hyperactive in brains of Fmr1 knockout mice, and inhibition of GSK3 by lithium administration ameliorates some behavioral impairment in these mice. We extended our studies of this association by testing whether GSK3 contributes to socialization behaviors. This used two mouse models with disrupted regulation of GSK3, Fmr1 knockout mice and GSK3 knockin mice, in which inhibitory serines of the two isoforms of GSK3, GSK3alpha and GSK3beta, are mutated to alanines, leaving GSK3 fully active.

METHODOLOGY/PRINCIPAL FINDINGS

To assess sociability, test mice were introduced to a restrained stimulus mouse (S1) for 10 min, followed by introduction of a second restrained stimulus mouse (S2) for 10 min, which assesses social preference. Fmr1 knockout and GSK3 knockin mice displayed no deficit in sociability with the S1 mouse, but unlike wild-type mice neither demonstrated social preference for the novel S2 mouse. Fmr1 knockout mice displayed more anxiety-related behaviors during social interaction (grooming, rearing, and digging) than wild-type mice, which was ameliorated by inhibition of GSK3 with chronic lithium treatment.

CONCLUSIONS/SIGNIFICANCE

These results indicate that impaired inhibitory regulation of GSK3 in Fmr1 knockout mice may contribute to some socialization deficits and that lithium treatment can ameliorate certain socialization impairments. As discussed in the present work, these results suggest a role for GSK3 in social behaviors and implicate inhibition of GSK3 as a potential therapeutic.

XIAP associates with GSK3 and inhibits the promotion of intrinsic apoptotic signaling by GSK3

This study examined if there are interactions between two key proteins that oppositely regulate intrinsic apoptosis, X-linked inhibitor of apoptosis protein (XIAP), a key suppressor of apoptosis that binds to inhibit active caspases, and glycogen synthase kinase-3 (GSK3), which promotes intrinsic apoptosis. Immunoprecipitation of GSK3beta revealed that XIAP associates with GSK3beta, as do two other members of the IAP family, cIAP-1, and cIAP-2. Cell fractionation revealed that XIAP is predominantly cytosolic, cIAP-1 is predominantly nuclear and nearly all of the nuclear cIAP-1 and cIAP-2 are associated with GSK3. Expression of individual domains of XIAP demonstrated that the RING domain of XIAP associates with GSK3. Inhibition of GSK3 did not alter the binding of XIAP to active caspase-9 or caspase-3 after stimulation of apoptosis with staurosporine. However, inhibition of GSK3 reduced apoptosis and apoptosome formation, including the recruitments of caspase-9 and XIAP to Apaf-1, in response to staurosporine treatment. Cell free measurements of apoptosome-induced caspase-3 activation demonstrated that GSK3 acts upstream of the apoptosome to facilitate intrinsic apoptotic signaling. This facilitation was blocked by overexpression of XIAP. These findings indicate that the RING domain of XIAP (and probably cIAP-1 and cIAP-2) associates with GSK3, GSK3 acts upstream of the apoptosome to promote intrinsic apoptosis, and the association between XIAP and GSK3 may block the pro-apoptotic function of GSK3.

Innate and adaptive immune responses regulated by glycogen synthase kinase-3 (GSK3)

In just a few years, the view of glycogen synthase kinase-3 (GSK3) has been transformed from an obscure enzyme seldom encountered in the immune literature to one implicated in an improbably large number of roles. GSK3 is a crucial regulator of the balance between pro- and anti-inflammatory cytokine production in both the periphery and the central nervous system, so that GSK3 inhibitors such as lithium can diminish inflammation. GSK3 influences T-cell proliferation, differentiation and survival. Many effects stem from GSK3 regulation of critical transcription factors, such as NF-kappaB, NFAT and STATs. These discoveries led to the rapid application of GSK3 inhibitors to animal models of sepsis, arthritis, colitis, multiple sclerosis and others, demonstrating their potential for therapeutic intervention.

Blocked inhibitory serine-phosphorylation of glycogen synthase kinase-3alpha/beta impairs in vivo neural precursor cell proliferation

BACKGROUND

Adult neurogenesis augments neuronal plasticity, and deficient neurogenesis might contribute to mood disorders and schizophrenia and impede treatment responses. Because these diseases might be associated with inadequately controlled glycogen synthase kinase-3 (GSK3), we tested whether blocked inhibitory serine-phosphorylation of GSK3 impairs neurogenesis.

METHODS

Neural precursor cell (NPC) proliferation was measured by dentate gyrus bromodeoxyuridine (BrdU) labeling in GSK3alpha/beta(21A/21A/9A/9A) knockin mice with serine-to-alanine mutations to block inhibitory serine-phosphorylation of GSK3 while it remains within the physiological range, because GSK3 is not overexpressed.

RESULTS

There was a drastic 40% impairment in neurogenesis in vivo in GSK3 knockin mice compared with wild-type mice. Impaired neurogenesis could be due to effects of GSK3 in NPCs or in surrounding cells that modulate NPCs. In vitro proliferation was equivalent for NPCs from GSK3 knockin and wild-type mice, suggesting an in vivo deficiency in GSK3 knockin mice of external support for NPC proliferation. Measurements of two neurotrophins that promote neurogenesis demonstrated less hippocampal vascular endothelial growth factor but not brain-derived growth factor in GSK3 knockin mice than wild-type mice, reinforcing the possibility that insufficient environmental support in GSK3 knockin mice might contribute to impaired neurogenesis. In vivo chronic co-administration of lithium and fluoxetine, which each increase inhibitory serine-phosphorylation of wild-type GSK3, increased NPC proliferation in wild-type but not GSK3 knockin mice.

CONCLUSIONS

Blocked inhibitory control of GSK3 impaired neurogenesis and the capacity of therapeutic drugs to stimulate neurogenesis, likely through deficient environmental factors that support neurogenesis, which might contribute to psychiatric diseases and responses to therapeutic drugs.

Glycogen synthase kinase-3 promotes the synergistic action of interferon-gamma on lipopolysaccharide-induced IL-6 production in RAW264.7 cells

Macrophages are the major effector cells of the innate immune system. Their function requires the integration of signals from pathogens, such as those induced by lipopolysaccharide (LPS), and from the host, such as those induced by interferon-gamma (IFN-gamma). The priming by IFN-gamma of Toll-like receptor-induced macrophage activation has long been recognized, but the mechanisms underlying this priming action remain unclear. We report in this study that the priming of macrophage-derived RAW264.7 cells by IFN-gamma is highly dependent on glycogen synthase kinase-3 (GSK3). Cooperative interactions of GSK3 and signal transducer and activator of transcription-3 (STAT3) were revealed by the findings that GSK3 inhibitors, or knockdown of the GSK3 beta isoform, strongly reduced the activation of STAT3, but not STAT1, induced by IFN-gamma without affecting upstream signaling events, and GSK3 was associated with STAT3. Direct inhibition of STAT3 activation abolished the synergistic action of IL-6 production by IFN-gamma administered with LPS. Similarly, inhibition of GSK3 abolished the synergistic stimulation of IFN-gamma on IL-6 production, and GSK3 was recruited to the IFN-gamma receptor by co-treatment with IFN-gamma and LPS. These results demonstrate the dependency of macrophage priming by IFN-gamma on STAT3 and GSK3, providing novel targets for intervention.

Lipopolysaccharide-induced interleukin-6 production is controlled by glycogen synthase kinase-3 and STAT3 in the brain

Background

Septic shock is a prevalent condition that, when not lethal, often causes disturbances in cognition, mood, and behavior, particularly due to central actions of the inflammatory cytokine interleukin-6 (IL-6). To identify potential targets to control brain IL-6, we tested if IL-6 produced by glia is regulated by signal transducer and activator of transcription-3 (STAT3) and glycogen synthase kinase-3 (GSK3).

Methods

Lipopolysaccharide (LPS) was used to induce inflammatory responses in mice or cultured primary glia. IL-6 was measured by ELISA and other inflammatory molecules were measured using an array.

Results

Mouse brain IL-6 levels increased after central, as well as peripheral, LPS administration, consistent with glia producing a portion of brain IL-6. STAT3 in the brain was activated after peripheral or central LPS administration, and in LPS-stimulated cultured primary glia. Inhibition of STAT3 expression, function, or activation reduced by ~80% IL-6 production by primary glia, demonstrating the dependence on active STAT3. GSK3 promotes STAT3 activation, and array analysis of inflammatory molecules produced by LPS-stimulated primary glia demonstrated that IL-6 was the cytokine most diminished (>90%) by GSK3 inhibition. Inhibition of GSK3, and knockdown of GSK3β, not GSK3α, greatly inhibited IL-6 production by LPS-stimulated primary glia. Conversely, expression of active STAT3 and active GSK3 promoted IL-6 production. In vivo inhibition of GSK3 reduced serum and brain IL-6 levels, brain STAT3 activation, and GFAP upregulation following LPS administration.

Conclusion

STAT3 and GSK3 cooperatively promote neuroinflammation, providing novel targets for anti-inflammatory intervention.

Forkhead box, class O transcription factors in brain: regulation and behavioral manifestation

BACKGROUND

The mammalian forkhead box, class O (FoxO) transcription factors function to regulate diverse physiological processes. Emerging evidence that both brain-derived neurotrophic factor (BDNF) and lithium suppress FoxO activity suggests a potential role of FoxOs in regulating mood-relevant behavior. Here, we investigated whether brain FoxO1 and FoxO3a can be regulated by serotonin and antidepressant treatment and whether their genetic deletion affects behaviors.

METHODS

C57BL/6 mice were treated with D-fenfluramine to increase brain serotonergic activity or with the antidepressant imipramine. The functional status of brain FoxO1 and FoxO3a was audited by immunoblot analysis for phosphorylation and subcellular localization. The behavioral manifestations in FoxO1- and FoxO3a-deficient mice were assessed via the Elevated Plus Maze Test, Forced Swim Test, Tail Suspension Test, and Open Field Test.

RESULTS

Increasing serotonergic activity by d-fenfluramine strongly increased phosphorylation of FoxO1 and FoxO3a in several brain regions and reduced nuclear FoxO1 and FoxO3a. The effect of D-fenfluramine was mediated by the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Chronic, but not acute, treatment with the antidepressant imipramine also increased the phosphorylation of brain FoxO1 and FoxO3a. When FoxO1 was selectively deleted from brain, mice displayed reduced anxiety. In contrast, FoxO3a-deficient mice presented with a significant antidepressant-like behavior.

CONCLUSIONS

FoxOs may be a transcriptional target for anxiety and mood disorder treatment. Despite their physical and functional relatedness, FoxO1 and FoxO3a influence distinct behavioral processes linked to anxiety and depression. Findings in this study reveal important new roles of FoxOs in brain and provide a molecular framework for further investigation of how FoxOs may govern mood and anxiety disorders.

Glycogen synthase kinase-3 regulates microglial migration, inflammation, and inflammation-induced neurotoxicity

Microglia play a prominent role in the brain's inflammatory response to injury or infection by migrating to affected locations, secreting inflammatory molecules, and phagocytosing damaged tissue. However, because severe or chronic neuroinflammation exacerbates many neurological conditions, controlling microglia actions may provide therapeutic benefits in a diverse array of diseases. Since glycogen synthase kinase-3 (GSK3) promotes inflammatory responses in peripheral immune cells, we investigated if inhibitors of GSK3 attenuated microglia responses to inflammatory stimuli. Treatment of BV-2 microglia with GSK3 inhibitors greatly reduced the migration of microglia in both a scratch assay and in a transwell migration assay. Treatment of BV-2 microglia with lipopolysaccharide (LPS) stimulated the production of interleukin-6 and increased the expression of inducible nitric oxide synthase (iNOS) and NO production. Each of these microglia responses to inflammatory stimulation were greatly attenuated by GSK3 inhibitors. However, GSK3 inhibitors did not cause a general impairment of microglia functions, as the LPS-induced stimulated expression of cyclooxygenase-2 was unaltered. Regulation of microglia functions were also evident in cultured mouse hippocampal slices where GSK3 inhibitors reduced cytokine production and microglial migration, and provided protection from inflammation-induced neuronal toxicity. These findings demonstrate that GSK3 promotes microglial responses to inflammation and that the utilization of GSK3 inhibitors provides a means to limit the inflammatory actions of microglia.