Altered GSK3β signaling in an infection-based mouse model of developmental neuropsychiatric disease

New insights into the role of GSK-3β in the brain: from neurodegenerative disease to tumorigenesis

Glycogen synthase kinase 3 (GSK-3) is a serine/threonine kinase widely expressed in various tissues and organs. Unlike other kinases, GSK-3 is active under resting conditions and is inactivated upon stimulation. In mammals, GSK-3 includes GSK-3 α and GSK-3β isoforms encoded by two homologous genes, namely, GSK3A and GSK3B. GSK-3β is essential for the control of glucose metabolism, signal transduction, and tissue homeostasis. As more than 100 known proteins have been identified as GSK-3β substrates, it is sometimes referred to as a moonlighting kinase. Previous studies have elucidated the regulation modes of GSK-3β. GSK-3β is involved in almost all aspects of brain functions, such as neuronal morphology, synapse formation, neuroinflammation, and neurological disorders. Recently, several comparatively specific small molecules have facilitated the chemical manipulation of this enzyme within cellular systems, leading to the discovery of novel inhibitors for GSK-3β. Despite these advancements, the therapeutic significance of GSK-3β as a drug target is still complicated by uncertainties surrounding the potential of inhibitors to stimulate tumorigenesis. This review provides a comprehensive overview of the intricate mechanisms of this enzyme and evaluates the existing evidence regarding the therapeutic potential of GSK-3β in brain diseases, including Alzheimer's disease, Parkinson's disease, mood disorders, and glioblastoma.

Group I mGluRs positive allosteric modulators improved schizophrenia-related behavioral and molecular deficits in the Poly I:C rat model

RATIONALE

Maternal polyinosinic-polycytidylic acid (Poly I:C) exposure leads to an increase in various proinflammatory cytokines and causes schizophrenia-like symptoms in offspring. In recent years, group I metabotropic glutamate receptors (mGluRs) have emerged as a potential target in the pathophysiology of schizophrenia.

OBJECTIVES

The aim of our study was to investigate the behavioral and molecular changes by using the mGlu1 receptor positive allosteric modulator (PAM) agent RO 67-7476, and the negative allosteric modulator (NAM) agent JNJ 16259685 and the mGlu5 receptor PAM agent VU-29, and NAM agent fenobam in the Poly I:C-induced schizophrenia model in rats.

METHODS

Female Wistar albino rats were treated with Poly I:C on day 14 of gestation after mating. On the postnatal day (PND) 35, 56 and 84, behavioral tests were performed in the male offspring. On the PND84, brain tissue was collected and the level of proinflammatory cytokines was determined by ELISA method.

RESULTS

Poly I:C caused impairments in all behavioral tests and increased the levels of proinflammatory cytokines. While PAM agents caused significant improvements in prepulse inhibition (PPI), novel object recognition (NOR), spontaneous alternation and reference memory tests, they brought the levels of proinflammatory cytokines closer to the control group. NAM agents were ineffective on behavioral tests. It was observed that PAM agents significantly improved Poly I:C-induced disruption in behavioral and molecular analyses.

CONCLUSIONS

These results suggest that PAM agents, particularly the mGlu5 receptor VU-29, are also promising and could be a potential target in schizophrenia.

Maternal immune activation impairs endocannabinoid signaling in the mesolimbic system of adolescent male offspring

Prenatal infections can increase the risk of developing psychiatric disorders such as schizophrenia in the offspring, especially when combined with other postnatal insults. Here, we tested, in a rat model of prenatal immune challenge by the viral mimic polyriboinosinic-polyribocytidilic acid, whether maternal immune activation (MIA) affects the endocannabinoid system and endocannabinoid-mediated modulation of dopamine functions. Experiments were performed during adolescence to assess i) the behavioral endophenotype (locomotor activity, plus maze, prepulse inhibition of startle reflex); ii) the locomotor activity in response to Δ9-Tetrahydrocannabinol (THC) and iii) the properties of ventral tegmental area (VTA) dopamine neurons in vivo and their response to THC; iv) endocannabinoid-mediated synaptic plasticity in VTA dopamine neurons; v) the expression of cannabinoid receptors and enzymes involved in endocannabinoid synthesis and catabolism in mesolimbic structures and vi) MIA-induced neuroinflammatory scenario evaluated by measurements of levels of cytokine and neuroinflammation markers. We revealed that MIA offspring displayed an altered locomotor activity in response to THC, a higher bursting activity of VTA dopamine neurons and a lack of response to cumulative doses of THC. Consistently, MIA adolescence offspring showed an enhanced 2-arachidonoylglycerol-mediated synaptic plasticity and decreased monoacylglycerol lipase activity in mesolimbic structures. Moreover, they displayed a higher expression of cyclooxygenase 2 (COX-2) and ionized calcium-binding adaptor molecule 1 (IBA-1), associated with latent inflammation and persistent microglia activity. In conclusion, we unveiled neurobiological mechanisms whereby inflammation caused by MIA influences the proper development of endocannabinoid signaling that negatively impacts the dopamine system, eventually leading to psychotic-like symptoms in adulthood.

Effects of Risperidone and Prenatal Poly I:C Exposure on GABAA Receptors and AKT-GSK3β Pathway in the Ventral Tegmental Area of Female Juvenile Rats

The ventral tegmental area (VTA) in the ventral midbrain is the origin of the dopaminergic neurotransmission pathways. Although GABA_A receptors and AKT-GSK3β signaling are involved in the pathophysiology of mental disorders and are modulated by antipsychotics, an unmet task is to reveal the pathological changes in these biomarkers and antipsychotic modulations in the VTA. Using a juvenile polyriboinosinic-polyribocytidylic acid (Poly I:C) psychiatric rat model, this study investigated the effects of adolescent risperidone treatment on GABA_A receptors and AKT/GSK3β in the VTA. Pregnant female Sprague-Dawley rats were administered Poly I:C (5mg/kg; i.p) or saline at gestational day 15. Juvenile female offspring received risperidone (0.9 mg/kg, twice per day) or a vehicle from postnatal day 35 for 25 days. Poly I:C offspring had significantly decreased mRNA expression of GABA_A receptor β3 subunits and glutamic acid decarboxylase (GAD2) in the VTA, while risperidone partially reversed the decreased GAD2 expression. Prenatal Poly I:C exposure led to increased expression of AKT2 and GSK3β. Risperidone decreased GABA_A receptor β2/3, but increased AKT2 mRNA expression in the VTA of healthy rats. This study suggests that Poly I:C-elicited maternal immune activation and risperidone differentially modulate GABAergic neurotransmission and AKT-GSK3β signaling in the VTA of adolescent rats.

Preclinical animal models of mental illnesses to translate findings from the bench to the bedside: Molecular brain mechanisms and peripheral biomarkers associated to early life stress or immune challenges

Animal models are useful preclinical tools for studying the pathogenesis of mental disorders and the effectiveness of their treatment. While it is not possible to mimic all symptoms occurring in humans, it is however possible to investigate the behavioral, physiological and neuroanatomical alterations relevant for these complex disorders in controlled conditions and in genetically homogeneous populations. Stressful and infection-related exposures represent the most employed environmental risk factors able to trigger or to unmask a psychopathological phenotype in animals. Indeed, when occurring during sensitive periods of brain maturation, including pre, postnatal life and adolescence, they can affect the offspring's neurodevelopmental trajectories, increasing the risk for mental disorders. Not all stressed or immune challenged animals, however, develop behavioral alterations and preclinical animal models can explain differences between vulnerable or resilient phenotypes. Our review focuses on different paradigms of stress (prenatal stress, maternal separation, social isolation and social defeat stress) and immune challenges (immune activation in pregnancy) and investigates the subsequent alterations in several biological and behavioral domains at different time points of animals' life. It also discusses the "double-hit" hypothesis where an initial early adverse event can prime the response to a second negative challenge. Interestingly, stress and infections early in life induce the activation of the hypothalamic-pituitary-adrenal (HPA) axis, alter the levels of neurotransmitters, neurotrophins and pro-inflammatory cytokines and affect the functions of microglia and oxidative stress. In conclusion, animal models allow shedding light on the pathophysiology of human mental illnesses and discovering novel molecular drug targets for personalized treatments.

Maternal immune activation in rodent models: A systematic review of neurodevelopmental changes in gene expression and epigenetic modulation in the offspring brain

Maternal immune activation (mIA) during pregnancy is hypothesised to disrupt offspring neurodevelopment and predispose offspring to neurodevelopmental disorders such as schizophrenia. Rodent models of mIA have explored possible mechanisms underlying this paradigm and provide a vital tool for preclinical research. However, a comprehensive analysis of the molecular changes that occur in mIA-models is lacking, hindering identification of robust clinical targets. This systematic review assesses mIA-driven transcriptomic and epigenomic alterations in specific offspring brain regions. Across 118 studies, we focus on 88 candidate genes and show replicated changes in expression in critical functional areas, including elevated inflammatory markers, and reduced myelin and GABAergic signalling proteins. Further, disturbed epigenetic markers at nine of these genes support mIA-driven epigenetic modulation of transcription. Overall, our results demonstrate that current outcome measures have direct relevance for the hypothesised pathology of schizophrenia and emphasise the importance of mIA-models in contributing to the understanding of biological pathways impacted by mIA and the discovery of new drug targets.

Reduction of dopamine and glycogen synthase kinase-3 signaling in rat striatum after continuous administration of haloperidol

BACKGROUND

Some individuals with schizophrenia present with a dopamine supersensitivity state (DSS) induced by a long-term administration of excessive antipsychotics; this is recognized as dopamine supersensitivity psychosis (DSP). The mechanisms underlying DSP are not established. Here, we investigated dopamine signaling in DSS rats.

METHODS

Haloperidol (HAL; 0.75 mg/kg/day for 14 days) or vehicle was administered to rats via an osmotic mini-pump. We then screened DSS rats from HAL-treated rats by a voluntary locomotion test. The striatal levels of dopamine (DA) and its metabolites 3,4-hydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined, as were the levels of protein kinase v-akt murine thymoma viral oncogene homolog (AKT), glycogen synthase kinase-3 (GSK-3), and phosphorylated GSK-3 in the striatal regions.

RESULTS

In the DSS rats, the DA, DOPAC, and HVA levels were significantly decreased. In a western blot analysis, the DSS rats exhibited a significant decrease in GSK-3α/β and an increase in the pGSK-3β/GSK-3β ratio, whereas AKT was not changed.

CONCLUSIONS

Our results indicated that the DSS rats had hypofunction of the basal dopamine release and AKT/GSK-3 signaling even at 7 days after the antipsychotic was discontinued. Protracted reductions in pre- and post-dopamine D2 receptor signaling might cause prolonged DSS.

Lithium Pharmacology and a Potential Role of Lithium on Methamphetamine Abuse and Dependence

BACKGROUND

The effectiveness of lithium salts in neuropsychiatric disorders such as bipolar disorder, Alzheimer's disease, and treatment-resistant depression has been documented in an extensive scientific literature. Lithium inhibits inositol monophosphatase, inositol polyphosphate 1- phosphatase, and glycogen synthase kinase-3 and decreases expression level of tryptophan hydroxylase 2, conceivably underlying the mood stabilizing effects of lithium, as well as procognitive and neuroprotective effects. However, the exact molecular mechanisms of action of lithium on mood stabilizing and pro-cognitive effects in humans are still largely unknown.

OBJECTIVE

On the basis of the known aspects of lithium pharmacology, this review will discuss the possible mechanisms underlying the therapeutic effects of lithium on positive symptoms of methamphetamine abuse and dependence.

CONCLUSION

It is possible that lithium treatment reduces the amount of newly synthesized phosphatidylinositol, potentially preventing or reversing neuroadaptations contributing to behavioral sensitization induced by methamphetamine. In addition, it is suggested that exposure to repeated doses of methamphetamine induces hyperactivation of glycogen synthase kinase-3β in the nucleus accumbens and in dorsal hippocampus, resulting in a long-term alterations in synaptic plasticity underlying behavioral sensitization as well as other behavioral deficits in memory-related behavior. Therefore it is clear that glycogen synthase kinase-3β inhibitors can be considered as a potential candidate for the treatment of methamphetamine abuse and dependence.

Maternal Type-I interferon signaling adversely affects the microglia and the behavior of the offspring accompanied by increased sensitivity to stress

Viral infection during pregnancy is often associated with neuropsychiatric conditions. In mice, exposure of pregnant dams to the viral mimetic poly(I:C), serves as a model that simulates such pathology in the offspring, through a process known as Maternal Immune Activation (MIA). To investigate the mechanism of such effect, we hypothesized that maternal upregulation of Type-I interferon (IFN-I), as part of the dam's antiviral response, might contribute to the damage imposed on the offspring. Using mRNA sequencing and flow cytometry analyses we found that poly(I:C) treatment during pregnancy caused reduced expression of genes related to proliferation and cell cycle in the offspring's microglia relative to controls. This was found to be associated with an IFN-I signature in the embryonic yolk sac, the origin of microglia in development. Neutralizing IFN-I signaling in dams attenuated the effect of MIA on the newborn's microglia, while systemic maternal administration of IFNβ was sufficient to mimic the effect of poly(I:C), and led to increased vulnerability of offspring's microglia to subsequent stress. Furthermore, maternal elevation of IFNβ resulted in behavioral manifestations reminiscent of neuropsychiatric disorders. In addition, by adopting a "two-hit" experimental paradigm, we show a higher sensitivity of the offspring to postnatal stress subsequent to the maternal IFNβ elevation, demonstrated by behavioral irregularities. Our results suggest that maternal upregulation of IFN-I, in response to MIA, interferes with the offspring's programmed microglial developmental cascade, increases their susceptibility to postnatal stress, and leads to behavioral abnormalities.

Maternal Immune Activation by Poly I:C as a preclinical Model for Neurodevelopmental Disorders: A focus on Autism and Schizophrenia

Maternal immune activation (MIA) in response to a viral infection during early and mid-gestation has been linked through various epidemiological studies to a higher risk for the child to develop autism or schizophrenia-related symptoms.. This has led to the establishment of the pathogen-free poly I:C-induced MIA animal model for neurodevelopmental disorders, which shows relatively high construct and face validity. Depending on the experimental variables, particularly the timing of poly I:C administration, different behavioural and molecular phenotypes have been described that relate to specific symptoms of neurodevelopmental disorders such as autism spectrum disorder and/or schizophrenia. We here review and summarize epidemiological evidence for the effects of maternal infection and immune activation, as well as major findings in different poly I:C MIA models with a focus on poly I:C exposure timing, behavioural and molecular changes in the offspring, and characteristics of the model that relate it to autism spectrum disorder and schizophrenia.

Maternal Immune Activation and the Development of Dopaminergic Neurotransmission of the Offspring: Relevance for Schizophrenia and Other Psychoses

Prenatal infections have been linked to the development of schizophrenia (SCZ) and other neurodevelopmental disorders in the offspring, and work in animal models indicates that this is to occur through the maternal inflammatory response triggered by infection. Several studies in animal models demonstrated that acute inflammatory episodes are sufficient to trigger brain alterations in the adult offspring, especially in the mesolimbic dopamine (DA) system, involved in the pathophysiology of SCZ and other disorders involving psychosis. In the current review, we synthesize the literature on the clinical studies implicating prenatal infectious events in the development of SCZ. Then, we summarize evidence from animal models of maternal immune activation (MIA) and the behavioral and molecular alterations relevant for the function of the DAergic system. Furthermore, we discuss the evidence supporting the involvement of maternal cytokines, such as interleukin 6 (IL-6) and leptin (a hormone with effects on inflammation) in mediating the effects of MIA on the fetal brain, leading to the long-lasting effects on the offspring. In particular, IL-6 has been involved in mediating the effects of MIA animal models in the offspring through actions on the placenta, induction of IL-17a, or triggering the decrease in non-heme iron (hypoferremia). Maternal infection is very likely interacting with additional genetic and environmental risk factors in the development of SCZ; systematically investigating how these interactions produce specific phenotypes is the next step in understanding the etiology of complex psychiatric disorders.

Inter-α-inhibitor deficiency in the mouse is associated with alterations in anxiety-like behavior, exploration and social approach

In recent years, several genome-wide association studies have identified candidate regions for genetic susceptibility in major mood disorders. Most notable are regions in a locus in chromosome 3p21, encompassing the genes NEK4-ITIH1-ITIH3-ITIH4. Three of these genes represent heavy chains of the composite protein inter-α-inhibitor (IαI). In order to further establish associations of these genes with mood disorders, we evaluated behavioral phenotypes in mice deficient in either Ambp/bikunin, which is necessary for functional ITIH1 and ITIH3 complexes, or in Itih4, the gene encoding the heavy chain Itih4. We found that loss of Itih4 had no effect on the behaviors tested, but loss of Ambp/bikunin led to increased anxiety-like behavior in the light/dark and open field tests and reduced exploratory activity in the elevated plus maze, light/dark preference and open field tests. Ambp/bikunin knockout mice also exhibited a sex-dependent exaggeration of acoustic startle responses, alterations in social approach during a three-chamber choice test, and an elevated fear conditioning response. These results provide experimental support for the role of ITIH1/ITIH3 in the development of mood disorders.

Brain changes in a maternal immune activation model of neurodevelopmental brain disorders

The developing brain is sensitive to a variety of insults. Epidemiological studies have identified prenatal exposure to infection as a risk factor for a range of neurological disorders, including autism spectrum disorder and schizophrenia. Animal models corroborate this association and have been used to probe the contribution of gene-environment interactions to the etiology of neurodevelopmental disorders. Here we review the behavior and brain phenotypes that have been characterized in MIA offspring, including the studies that have looked at the interaction between maternal immune activation and genetic risk factors for autism spectrum disorder or schizophrenia. These phenotypes include behaviors relevant to autism, schizophrenia, and other neurological disorders, alterations in brain anatomy, and structural and functional neuronal impairments. The link between maternal infection and these phenotypic changes is not fully understood, but there is increasing evidence that maternal immune activation induces prolonged immune alterations in the offspring's brain which could underlie epigenetic alterations which in turn may mediate the behavior and brain changes. These concepts will be discussed followed by a summary of the pharmacological interventions that have been tested in the maternal immune activation model.

Mouse models of maternal immune activation: Mind your caging system!

Rodent models of maternal immune activation (MIA) are increasingly used as experimental tools to study neuronal and behavioral dysfunctions in relation to infection-mediated neurodevelopmental disorders. One of the most widely used MIA models is based on gestational administration of poly(I:C) (= polyriboinosinic-polyribocytdilic acid), a synthetic analog of double-stranded RNA that induces a cytokine-associated viral-like acute phase response. The effects of poly(I:C)-induced MIA on phenotypic changes in the offspring are known to be influenced by various factors, including the precise prenatal timing, genetic background, and immune stimulus intensity. Thus far, however, it has been largely ignored whether differences in the basic type of laboratory housing can similarly affect the outcomes of MIA models. Here, we examined this possibility by comparing the poly(I:C)-based MIA model in two housing systems that are commonly used in preclinical mouse research, namely the open cage (OC) and individually ventilated cage (IVC) systems. Pregnant C57BL6/N mice were kept in OCs or IVCs and treated with a low (1 mg/kg, i.v.) or high (5 mg/kg, i.v.) dose of poly(I:C), or with control vehicle solution. MIA or control treatment was induced on gestation day (GD) 9 or 12, and the resulting offspring were raised and maintained in OCs or IVCs until adulthood for behavioral testing. An additional cohort of dams was used to assess the influence of the different caging systems on poly(I:C)-induced cytokine and stress responses in the maternal plasma. Maternal poly(I:C) administration on GD9 caused a dose-dependent increase in spontaneous abortion in IVCs but not in OCs, whereas MIA in IVC systems during a later gestational time-point (GD12) did not affect pregnancy outcomes. Moreover, the precise type of caging system markedly affected maternal cytokines and chemokines at basal states and in response to poly(I:C) and further influenced the maternal levels of the stress hormone, corticosterone. The efficacy of MIA to induce deficits in working memory, social interaction, and sensorimotor gating in the adult offspring was influenced by the different housing conditions, the dosing of poly(I:C), and the precise prenatal timing. Taken together, the present study identifies the basic type of caging system as a novel factor that can confound the outcomes of MIA in mice. Our findings thus urge the need to consider and report the kind of laboratory housing systems used to implement MIA models. Providing this information seems pivotal to yield reproducible results in these models.

Controversies and prospects about microglia in maternal immune activation models for neurodevelopmental disorders

Activation of the maternal immune system during pregnancy is a well-established risk factor for neuropsychiatric disease in the offspring, yet, the underlying mechanisms leading to altered brain function remain largely undefined. Microglia, the resident immune cells of the brain, are key to adequate development of the central nervous system (CNS), and are prime candidates to mediate maternal immune activation (MIA)-induced brain abnormalities. As such, the effects of MIA on the immunological phenotype of microglia has been widely investigated. However, contradicting results due to differences in read-out and methodological approaches impede final conclusions on MIA-induced microglial alterations. The aim of this review is to critically discuss the evidence for an activated microglial phenotype upon MIA.

Late gestation immune activation increases IBA1-positive immunoreactivity levels in the corpus callosum of adult rat offspring

Animal models of maternal immune activation study the effects of infection, an environmental risk factor for schizophrenia, on brain development. Microglia activation and cytokine upregulation may have key roles in schizophrenia neuropathology. We hypothesised that maternal immune activation induces changes in microglia and cytokines in the brains of the adult offspring. Maternal immune activation was induced by injecting polyriboinosinic:polyribocytidylic acid into pregnant rats on gestational day (GD) 10 or GD19, with brain tissue collected from the offspring at adulthood. We observed no change in Iba1, Gfap, IL1-β and TNF-α mRNA levels in the cingulate cortex (CC) in adult offspring exposed to maternal immune activation. Prenatal exposure to immune activation had a significant main effect on microglial IBA1-positive immunoreactive material (IBA1+IRM) in the corpus callosum; post-hoc analyses identified a significant increase in GD19 offspring, but not GD10. No change in was observed in the CC. In contrast, maternal immune activation had a significant main effect on GFAP+IRM in the CC at GD19 (not GD10); post-hoc analyses only identified a strong trend towards increased GFAP+IRM in the GD19 offspring, with no white matter changes. This suggests late gestation maternal immune activation causes subtle alterations to microglia and astrocytes in the adult offspring.

Translocator protein (TSPO) and stress cascades in mouse models of psychosis with inflammatory disturbances

Changes in inflammatory cascades have been implicated in the underlying pathophysiology of psychosis. Translocator protein 18 kDa (TSPO) has been used to assess neuroinflammatory processes in psychotic disorders. Nonetheless, it is unclear whether TSPO, a mitochondrial protein, can be interpreted as a general marker for inflammation in diseases involving psychosis. To address this question, we investigated TSPO signaling in representative mouse models for psychosis with inflammatory disturbances. The maternal immune activation and cuprizone short-term exposure models show different TSPO signaling. Furthermore, we observed similarities and differences in their respective stress pathways including stress hormone signaling and oxidative stress that are functionally interconnected with the inflammatory responses. We propose that more careful studies of TSPO distribution in neuroinflammation and other stress cascades associated with psychotic symptoms will allow us to understand the biological mechanisms underlying psychosis-related behaviors.

Maternal Immune Activation Causes Behavioral Impairments and Altered Cerebellar Cytokine and Synaptic Protein Expression

Emerging epidemiology studies indicate that maternal immune activation (MIA) resulting from inflammatory stimuli such as viral or bacterial infections during pregnancy serves as a risk factor for multiple neurodevelopmental disorders including autism spectrum disorders and schizophrenia. Although alterations in the cortex and hippocampus of MIA offspring have been described, less evidence exists on the impact on the cerebellum. Here, we report altered expression of cytokines and chemokines in the cerebellum of MIA offspring, including increase in the neuroinflammatory cytokine TNFα and its receptor TNFR1. We also report reduced expression of the synaptic organizing proteins cerebellin-1 and GluRδ2. These synaptic protein alterations are associated with a deficit in the ability of cerebellar neurons to form synapses and an increased number of dendritic spines that are not in contact with a presynaptic terminal. These impairments are likely contributing to the behavioral deficits in the MIA exposed offspring.

Prenatal immune activation causes hippocampal synaptic deficits in the absence of overt microglia anomalies

Prenatal exposure to infectious or inflammatory insults can increase the risk of developing neuropsychiatric disorder in later life, including schizophrenia, bipolar disorder, and autism. These brain disorders are also characterized by pre- and postsynaptic deficits. Using a well-established mouse model of maternal exposure to the viral mimetic polyriboinosinic-polyribocytidilic acid [poly(I:C)], we examined whether prenatal immune activation might cause synaptic deficits in the hippocampal formation of pubescent and adult offspring. Based on the widely appreciated role of microglia in synaptic pruning, we further explored possible associations between synaptic deficits and microglia anomalies in offspring of poly(I:C)-exposed and control mothers. We found that prenatal immune activation induced an adult onset of presynaptic hippocampal deficits (as evaluated by synaptophysin and bassoon density). The early-life insult further caused postsynaptic hippocampal deficits in pubescence (as evaluated by PSD95 and SynGAP density), some of which persisted into adulthood. In contrast, prenatal immune activation did not change microglia (or astrocyte) density, nor did it alter their activation phenotypes. The prenatal manipulation did also not cause signs of persistent systemic inflammation. Despite the absence of overt glial anomalies or systemic inflammation, adult offspring exposed to prenatal immune activation displayed increased hippocampal IL-1β levels. Taken together, our findings demonstrate that age-dependent synaptic deficits and abnormal pro-inflammatory cytokine expression can occur during postnatal brain maturation in the absence of microglial anomalies or systemic inflammation.

Upregulation of GSK3β Contributes to Brain Disorders in Elderly REGγ-knockout Mice

GSK3β regulates some functions of the brain, but the mechanisms involved in the maintenance of GSK3β protein stability remain ambiguous. REGγ, an important proteasome activator for ubiquitin-independent protein degradation, has been shown to degrade certain intact proteins and is involved in the regulation of important biological processes. Here we demonstrate that REGγ promotes the degradation of GSK3β protein in vitro and in vivo. With increased GSK3β activity, REGγ knockout (REGγ-/-) mice exhibit late-onset sensorimotor gating and cognitive deficiencies including decreased working memory, hyperlocomotion, increased stereotype, defective prepulse inhibition (PPI), and disability in nest building, at the age of 8 months or older. Inhibition of GSK3β rescued the compromised PPI phenotypes and working memory deficiency in the knockout mice. Also, we found an age-dependent decrease in the trypsin-like proteasomal activity in REGγ-/- mice brains, which may be reflective of a lack of degradation of GSK3β. Collectively, our findings reveal a novel regulatory pathway in which the REGγ-proteasome controls the steady-state level of GSK3β protein. Dysfunction in this non-canonical proteasome degradation pathway may contribute to the sensorimotor gating deficiency and cognitive disorders in aging mice.

Alterations of Dopamine D2 Receptors and Related Receptor-Interacting Proteins in Schizophrenia: The Pivotal Position of Dopamine Supersensitivity Psychosis in Treatment-Resistant Schizophrenia

Although the dopamine D2 receptor (DRD2) has been a main target of antipsychotic pharmacotherapy for the treatment of schizophrenia, the standard treatment does not offer sufficient relief of symptoms to 20%-30% of patients suffering from this disorder. Moreover, over 80% of patients experience relapsed psychotic episodes within five years following treatment initiation. These data strongly suggest that the continuous blockade of DRD2 by antipsychotic(s) could eventually fail to control the psychosis in some point during long-term treatment, even if such treatment has successfully provided symptomatic improvement for the first-episode psychosis, or stability for the subsequent chronic stage. Dopamine supersensitivity psychosis (DSP) is historically known as a by-product of antipsychotic treatment in the manner of tardive dyskinesia or transient rebound psychosis. Numerous data in psychopharmacological studies suggest that the up-regulation of DRD2, caused by antipsychotic(s), is likely the mechanism underlying the development of the dopamine supersensitivity state. However, regardless of evolving notions of dopamine signaling, particularly dopamine release, signal transduction, and receptor recycling, most of this research has been conducted and discussed from the standpoint of disease etiology or action mechanism of the antipsychotic, not of DSP. Hence, the mechanism of the DRD2 up-regulation or mechanism evoking clinical DSP, both of which are caused by pharmacotherapy, remains unknown. Once patients experience a DSP episode, they become increasingly difficult to treat. Light was recently shed on a new aspect of DSP as a treatment-resistant factor. Clarification of the detailed mechanism of DSP is therefore crucial, and a preventive treatment strategy for DSP or treatment-resistant schizophrenia is urgently needed.

Late prenatal immune activation causes hippocampal deficits in the absence of persistent inflammation across aging

BACKGROUND

Prenatal exposure to infection and/or inflammation is increasingly recognized to play an important role in neurodevelopmental brain disorders. It has recently been postulated that prenatal immune activation, especially when occurring during late gestational stages, may also induce pathological brain aging via sustained effects on systemic and central inflammation. Here, we tested this hypothesis using an established mouse model of exposure to viral-like immune activation in late pregnancy.

METHODS

Pregnant C57BL6/J mice on gestation day 17 were treated with the viral mimetic polyriboinosinic-polyribocytidilic acid (poly(I:C)) or control vehicle solution. The resulting offspring were first tested using cognitive and behavioral paradigms known to be sensitive to hippocampal damage, after which they were assigned to quantitative analyses of inflammatory cytokines, microglia density and morphology, astrocyte density, presynaptic markers, and neurotrophin expression in the hippocampus throughout aging (1, 5, and 22 months of age).

RESULTS

Maternal poly(I:C) treatment led to a robust increase in inflammatory cytokine levels in late gestation but did not cause persistent systemic or hippocampal inflammation in the offspring. The late prenatal manipulation also failed to cause long-term changes in microglia density, morphology, or activation, and did not induce signs of astrogliosis in pubescent, adult, or aged offspring. Despite the lack of persistent inflammatory or glial anomalies, offspring of poly(I:C)-exposed mothers showed marked and partly age-dependent deficits in hippocampus-regulated cognitive functions as well as impaired hippocampal synaptophysin and brain-derived neurotrophic factor (BDNF) expression.

CONCLUSIONS

Late prenatal exposure to viral-like immune activation in mice causes hippocampus-related cognitive and synaptic deficits in the absence of chronic inflammation across aging. These findings do not support the hypothesis that this form of prenatal immune activation may induce pathological brain aging via sustained effects on systemic and central inflammation. We further conclude that poly(I:C)-based prenatal immune activation models are reliable in their effectiveness to induce (hippocampal) neuropathology across aging, but they appear unsuited for studying the role of chronic systemic or central inflammation in brain aging.

Impaired synaptic development in a maternal immune activation mouse model of neurodevelopmental disorders

Both genetic and environmental factors are thought to contribute to neurodevelopmental and neuropsychiatric disorders with maternal immune activation (MIA) being a risk factor for both autism spectrum disorders and schizophrenia. Although MIA mouse offspring exhibit behavioral impairments, the synaptic alterations in vivo that mediate these behaviors are not known. Here we employed in vivo multiphoton imaging to determine that in the cortex of young MIA offspring there is a reduction in number and turnover rates of dendritic spines, sites of majority of excitatory synaptic inputs. Significantly, spine impairments persisted into adulthood and correlated with increased repetitive behavior, an ASD relevant behavioral phenotype. Structural analysis of synaptic inputs revealed a reorganization of presynaptic inputs with a larger proportion of spines being contacted by both excitatory and inhibitory presynaptic terminals. These structural impairments were accompanied by altered excitatory and inhibitory synaptic transmission. Finally, we report that a postnatal treatment of MIA offspring with the anti-inflammatory drug ibudilast, prevented both synaptic and behavioral impairments. Our results suggest that a possible altered inflammatory state associated with maternal immune activation results in impaired synaptic development that persists into adulthood but which can be prevented with early anti-inflammatory treatment.

Long-term pathological consequences of prenatal infection: beyond brain disorders

Prenatal immunological adversities such as maternal infection have been widely acknowledged to contribute to an increased risk of neurodevelopmental brain disorders. In recent years, epidemiological and experimental evidence has accumulated to suggest that prenatal exposure to immune challenges can also negatively affect various physiological and metabolic functions beyond those typically associated with primary defects in CNS development. These peripheral changes include excessive accumulation of adipose tissue and increased body weight, impaired glycemic regulation and insulin resistance, altered myeloid lineage development, increased gut permeability, hyperpurinergia, and changes in microbiota composition. Experimental work in animal models further suggests that at least some of these peripheral abnormalities could directly contribute to CNS dysfunctions, so that normalization of peripheral pathologies could lead to an amelioration of behavioral deficits. Hence, seemingly unrelated central and peripheral effects of prenatal infection could represent interrelated pathological entities that emerge in response to a common developmental stressor. Targeting peripheral abnormalities may thus represent a valuable strategy to improve the wide spectrum of behavioral abnormalities that can emerge in subjects with prenatal infection histories.

The poly(I:C)-induced maternal immune activation model in preclinical neuropsychiatric drug discovery

Increasing epidemiological and experimental evidence implicates gestational infections as one important factor involved in the pathogenesis of several neuropsychiatric disorders. Corresponding preclinical model systems based upon maternal immune activation (MIA) by treatment of the pregnant female have been developed. These MIA animal model systems have been successfully used in basic and translational research approaches, contributing to the investigation of the underlying pathophysiological mechanisms at the molecular, cellular and behavioral levels. The present article focuses on the application of a specific MIA rodent paradigm, based upon treatment of the gestating dam with the viral mimic polyinosinic-polycytidilic acid (Poly(I:C)), a synthetic analog of double-stranded RNA (dsRNA) which activates the Toll-like receptor 3 (TLR3) pathway. Important advantages and constraints of this animal model will be discussed, specifically in light of gestational infection as one vulnerability factor contributing to the complex etiology of mood and psychotic disorders, which are likely the result of intricate multi-level gene×environment interactions. Improving our currently incomplete understanding of the molecular pathomechanistic principles underlying these disorders is a prerequisite for the development of alternative therapeutic approaches which are critically needed in light of the important drawbacks and limitations of currently available pharmacological treatment options regarding efficacy and side effects. The particular relevance of the Poly(I:C) MIA model for the discovery of novel drug targets for symptomatic and preventive therapeutic strategies in mood and psychotic disorders is highlighted in this review article.

Glycogen synthase kinase-3 beta (GSK-3β) signaling: Implications for Parkinson's disease

Glycogen synthase kinase 3 (GSK-3) dysregulation plays an important role in the pathogenesis of numerous disorders, affecting the central nervous system (CNS) encompassing both neuroinflammation and neurodegenerative diseases. Several lines of evidence have illustrated a key role of the GSK-3 and its cellular and molecular signaling cascades in the control of neuroinflammation. Glycogen synthase kinase 3 beta (GSK-3β), one of the GSK-3 isomers, plays a major role in neuronal apoptosis and its inhibition decreases expression of alpha-Synuclein (α-Synuclein), which make this kinase an attractive therapeutic target for neurodegenerative disorders. Parkinson's disease (PD) is a chronic neurodegenerative movement disorder characterized by the progressive and massive loss of dopaminergic neurons by neuronal apoptosis in the substantia nigra pars compacta and depletion of dopamine in the striatum, which lead to pathological and clinical abnormalities. Thus, understanding the role of GSK-3β in PD will enhance our knowledge of the basic mechanisms underlying the pathogenesis of this disorder and facilitate the identification of new therapeutic avenues. In recent years, GSK-3β has been shown to play essential roles in modulating a variety of cellular functions, which have prompted efforts to develop GSK-3β inhibitors as therapeutics. In this review, we summarize GSK-3 signaling pathways and its association with neuroinflammation. Moreover, we highlight the interaction between GSK-3β and several cellular processes involved in the pathogenesis of PD, including the accumulation of α-Synuclein aggregates, oxidative stress and mitochondrial dysfunction. Finally, we discuss about GSK-3β inhibitors as a potential therapeutic strategy in PD.

The effects of GSK-3β blockade on ketamine self-administration and relapse to drug-seeking behavior in rats

RATIONALE

The role of glycogen synthase kinase-3 (GSK-3) has recently been implicated in the neurochemical mechanism underlying ketamine-induced neuronal toxicity and behavioral disturbance.

OBJECTIVES

The primary goal of the present study was to determine the role of GSK-3β in ketamine self-administration (SA) and relapse to drug-seeking behavior after abstinence.

METHODS

In Experiment 1, the level of phosphorylated GSK-3β (p-GSK-3β) and total GSK-3β (t-GSK-3β) was determined in various brain areas following 14 days of ketamine SA. In Experiments 2 and 3, the effects of a GSK-3β inhibitor, SB216763 (2 and 4 mg/kg) and a GSK-3 inhibitor, lithium (LiCl, 100mg/kg) on the responding maintained by 0.5mg/kg/infusion ketamine SA were evaluated. In Experiments 4 and 5, rats underwent ketamine SA for 14 days followed by a 10-day abstinence period. The animals were treated with 2 or 4 mg/kg GSK-3β inhibitor, or 100mg/kg LiCl during the cue-induced relapse test. Seven days later, animals received the same drug treatment and underwent the drug-induced relapse test. Finally, the effect of saline and DMSO on locomotor activity was evaluated in Experiment 6.

RESULTS

Ketamine SA significantly decreased the ratio p-GSK-3β and t-GSK-3β (p-GSK-3β:t-GSK-3β) in the caudate putamen, nucleus accumbens, and ventral tegmental area. Both SB216763 and LiCl decreased responding on a progressive ratio schedule, but not on a fixed ratio schedule. Cue-induced relapse was suppressed only by 4mg/kg SB216763, whereas drug-induced relapse was inhibited by 2, 4 mg/kg SB216763 and LiCl. However, inactive responses were also suppressed by LiCl during progressive ratio and drug-induced relapse testing.

CONCLUSIONS

SB216763 was effective at decreasing ketamine SA under the PR schedule and reducing drug-seeking behavior after abstinence.

Effect of maternal immune activation on the kynurenine pathway in preadolescent rat offspring and on MK801-induced hyperlocomotion in adulthood: amelioration by COX-2 inhibition

Infections during pregnancy and subsequent maternal immune activation (MIA) increase risk for schizophrenia in offspring. The progeny of rodents injected with the viral infection mimic polyI:C during gestation display brain and behavioural abnormalities but the underlying mechanisms are unknown. Since the blood kynurenine pathway (KP) of tryptophan degradation impacts brain function and is strongly regulated by the immune system, we tested if KP changes occur in polyI:C offspring at preadolescence. We also tested whether MK801-induced hyperlocomotion, a behaviour characteristic of adult polyI:C offspring, is prevented by adolescent treatment with celecoxib, a COX-2 inhibitor that impacts the KP. Pregnant rats were treated with polyI:C (4mg/kg, i.v.) or vehicle on gestational day 19. Serum levels of KP metabolites were measured in offspring of polyI:C or vehicle treated dams at postnatal day (PND) 31-33 using HPLC/GCMS. Additional polyI:C or vehicle exposed offspring were given celecoxib or vehicle between PND 35 and 46 and tested with MK801 (0.3mg/kg) in adulthood (PND>90). Prenatal polyI:C resulted in increases in the serum KP neurotoxic metabolite quinolinic acid at PND 31-33 (105%, p=0.014). In contrast, the neuroprotective kynurenic acid and its precursor kynurenine were significantly decreased (28% p=0.027, and 31% p=0.033, respectively). Picolinic acid, another neuroprotective KP metabolite, was increased (31%, p=0.014). Adolescent treatment with celecoxib (2.5 and 5mg/kg/day, i.p.) prevented the development of MK801-induced hyperlocomotion in adult polyI:C offspring. Our study reveals the blood KP as a potential mechanism by which MIA interferes with postnatal brain maturation and associated behavioural disturbances and emphasises the preventative potential of inflammation targeting drugs.

Reversal of autism-like behaviors and metabolism in adult mice with single-dose antipurinergic therapy

Autism spectrum disorders (ASDs) now affect 1-2% of the children born in the United States. Hundreds of genetic, metabolic and environmental factors are known to increase the risk of ASD. Similar factors are known to influence the risk of schizophrenia and bipolar disorder; however, a unifying mechanistic explanation has remained elusive. Here we used the maternal immune activation (MIA) mouse model of neurodevelopmental and neuropsychiatric disorders to study the effects of a single dose of the antipurinergic drug suramin on the behavior and metabolism of adult animals. We found that disturbances in social behavior, novelty preference and metabolism are not permanent but are treatable with antipurinergic therapy (APT) in this model of ASD and schizophrenia. A single dose of suramin (20 mg kg(-1) intraperitoneally (i.p.)) given to 6-month-old adults restored normal social behavior, novelty preference and metabolism. Comprehensive metabolomic analysis identified purine metabolism as the key regulatory pathway. Correction of purine metabolism normalized 17 of 18 metabolic pathways that were disturbed in the MIA model. Two days after treatment, the suramin concentration in the plasma and brainstem was 7.64 μM pmol μl(-1) (±0.50) and 5.15 pmol mg(-1) (±0.49), respectively. These data show good uptake of suramin into the central nervous system at the level of the brainstem. Most of the improvements associated with APT were lost after 5 weeks of drug washout, consistent with the 1-week plasma half-life of suramin in mice. Our results show that purine metabolism is a master regulator of behavior and metabolism in the MIA model, and that single-dose APT with suramin acutely reverses these abnormalities, even in adults.

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.