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

Cadmium modulates intestinal Wnt/β-catenin signaling ensuing intestinal barrier disruption and systemic inflammation

The intricate architecture of the intestinal epithelium, crucial for nutrient absorption, is constantly threatened by environmental factors. The epithelium undergoes rapid turnover, which is essential for maintaining homeostasis, under the control of intestinal stem cells (ISCs). The central regulator, Wnt/β-catenin signaling plays a key role in intestinal integrity and turnover. Despite its significance, the impact of environmental factors on this pathway has been largely overlooked. This study, for the first time, investigates the influence of Cd on the intestinal Wnt signaling pathway using a mouse model. In this study, male BALB/c mice were administered an environmentally relevant Cd dose (0.98 mg/kg) through oral gavage to investigate the intestinal disruption and Wnt signaling pathway. Various studies, including histopathology, immunohistochemistry, RT-PCR, western blotting, ELISA, intestinal permeability assay, and flow cytometry, were conducted to study Cd-induced changes in the intestine. The canonical Wnt signaling pathway experienced significant downregulation as a result of sub-chronic Cd exposure, which caused extensive damage throughout the small intestine. Increased intestinal permeability and a skewed immune response were also observed. To confirm that Wnt signaling downregulation is the key driver of Cd-induced gastrointestinal toxicity, mice were co-exposed to LiCl (a recognized Wnt activator) and Cd. The results clearly showed that the harmful effects of Cd could be reversed, which is strong evidence that Cd mostly damages the intestine through the Wnt/β-catenin signalling axis. In conclusion, this research advances the current understanding of the role of Wnt/β catenin signaling in gastrointestinal toxicity caused by diverse environmental pollutants.

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Interactome analysis implicates class II transactivator (CIITA) in depression and other neuroinflammatory disorders

PURPOSE

Inappropriate inflammatory responses within the nervous system (neuroinflammation) have been implicated in several neurological conditions. Class II transactivator (CIITA), a principal regulator of the major histocompatibility complex II (MHCII), is known to play essential roles in inflammation. Hence, CIITA and its interactors could be potentially involved in multiple neurological disorders. However, the molecular mechanisms underlying CIITA-mediated neuroinflammation (NI) are yet to be understood.

MATERIALS AND METHODS

In this regard, we analyzed the potential involvement of CIITA and its interactome in the regulation of neuroinflammation. In the present study, using various computational tools, we aimed (1) to identify NI-related proteins, (2) to filter the critical interactors in the CIITA-NI network, and (3) to analyze the protein-disease interactions and the associated molecular pathways through which CIITA could influence neuroinflammation.

RESULTS

CIITA was found to interact with P T GS2, GSK3B, and NR3C1 and may influence depressive disorders. Further, the IL4/IL13 pathway was found to be potentially underlying the CIITA-interactomemediated effects on neurological disorders. Moreover, CIITA was found to be connected to genes associated with depressive disorder through IL4, wherein CIITA was found to be potentially involved in depressive disorders through IL-4/IL-13 and hippo pathways. However, the present study is based on the existing data on protein interactomes and could be re-evaluated as newer interactions are discovered. Also, the functional mechanisms of CIITA's roles in neuroinflammation must be evaluated further.

CONCLUSION

Notwithstanding these limitations, the results presented here, could form a basis for further experimental studies to assess CIITA as a potential therapeutic target in managing depression and other neuroinflammatory disorders.

CaMKK2 as an emerging treatment target for bipolar disorder

Current pharmacological treatments for bipolar disorder are inadequate and based on serendipitously discovered drugs often with limited efficacy, burdensome side-effects, and unclear mechanisms of action. Advances in drug development for the treatment of bipolar disorder remain incremental and have come largely from repurposing drugs used for other psychiatric conditions, a strategy that has failed to find truly revolutionary therapies, as it does not target the mood instability that characterises the condition. The lack of therapeutic innovation in the bipolar disorder field is largely due to a poor understanding of the underlying disease mechanisms and the consequent absence of validated drug targets. A compelling new treatment target is the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme. CaMKK2 is highly enriched in brain neurons and regulates energy metabolism and neuronal processes that underpin higher order functions such as long-term memory, mood, and other affective functions. Loss-of-function polymorphisms and a rare missense mutation in human CAMKK2 are associated with bipolar disorder, and genetic deletion of Camkk2 in mice causes bipolar-like behaviours similar to those in patients. Furthermore, these behaviours are ameliorated by lithium, which increases CaMKK2 activity. In this review, we discuss multiple convergent lines of evidence that support targeting of CaMKK2 as a new treatment strategy for bipolar disorder.

When You Come to a Fork in the Road, Take It: Wnt Signaling Activates Multiple Pathways through the APC/Axin/GSK-3 Complex

The Wnt signaling pathway is a highly conserved regulator of metazoan development and stem cell maintenance. Activation of Wnt signaling is an early step in diverse malignancies. Work over the past four decades has defined a "canonical" Wnt pathway that is initiated by Wnt proteins, secreted glycoproteins that bind to a surface receptor complex and activate intracellular signal transduction by inhibiting a catalytic complex composed of the classical tumor suppressor Adenomatous Polyposis Coli (APC), Axin, and Glycogen Synthase Kinase-3 (GSK-3). The best characterized effector of this complex is β-catenin, which is stabilized by inhibition of GSK-3, allowing β-catenin entrance to the nucleus and activation of Wnt target gene transcription, leading to multiple cancers when inappropriately activated. However, canonical Wnt signaling through the APC/Axin/GSK-3 complex impinges on other effectors, independently of β-catenin, including the mechanistic Target of Rapamycin (mTOR), regulators of protein stability, mitotic spindle orientation, and Hippo signaling. This review focuses on these alternative effectors of the canonical Wnt pathway and how they may contribute to cancers.

The histamine H3 receptor modulates dopamine D2 receptor-dependent signaling pathways and mouse behaviors

The histamine H3 receptor (H3R) is highly enriched in the spiny projection neurons (SPNs) of the striatum, in both the D1 receptor (D1R)-expressing and D2 receptor (D2R)-expressing populations. A crossantagonistic interaction between H3R and D1R has been demonstrated in mice, both at the behavioral level and at the biochemical level. Although interactive behavioral effects have been described upon coactivation of H3R and D2R, the molecular mechanisms underlying this interaction are poorly understood. Here, we show that activation of H3R with the selective agonist R-(-)-α-methylhistamine dihydrobromide mitigates D2R agonist-induced locomotor activity and stereotypic behavior. Using biochemical approaches and the proximity ligation assay, we demonstrated the existence of an H3R-D2R complex in the mouse striatum. In addition, we examined consequences of simultaneous H3R-D2R agonism on the phosphorylation levels of several signaling molecules using immunohistochemistry. H3R agonist treatment modulated Akt (serine/threonine PKB)-glycogen synthase kinase 3 beta signaling in response to D2R activation via a β-arrestin 2-dependent mechanism in D2R-SPNs but not in D1R-SPNs. Phosphorylation of mitogen- and stress-activated protein kinase 1 and rpS6 (ribosomal protein S6) was largely unchanged under these conditions. As Akt-glycogen synthase kinase 3 beta signaling has been implicated in several neuropsychiatric disorders, this work may help clarify the role of H3R in modulating D2R function, leading to a better understanding of pathophysiology involving the interaction between histamine and dopamine systems.

Inhibition of glycogen synthase kinase 3 by lithium, a mechanism in search of specificity

Inhibition of Glycogen synthase kinase 3 (GSK3) is a popular explanation for the effects of lithium ions on mood regulation in bipolar disorder and other mental illnesses, including major depression, cyclothymia, and schizophrenia. Contribution of GSK3 is supported by evidence obtained from animal and patient derived model systems. However, the two GSK3 enzymes, GSK3α and GSK3β, have more than 100 validated substrates. They are thus central hubs for major biological functions, such as dopamine-glutamate neurotransmission, synaptic plasticity (Hebbian and homeostatic), inflammation, circadian regulation, protein synthesis, metabolism, inflammation, and mitochondrial functions. The intricate contributions of GSK3 to several biological processes make it difficult to identify specific mechanisms of mood stabilization for therapeutic development. Identification of GSK3 substrates involved in lithium therapeutic action is thus critical. We provide an overview of GSK3 biological functions and substrates for which there is evidence for a contribution to lithium effects. A particular focus is given to four of these: the transcription factor cAMP response element-binding protein (CREB), the RNA-binding protein FXR1, kinesin subunits, and the cytoskeletal regulator CRMP2. An overview of how co-regulation of these substrates may result in shared outcomes is also presented. Better understanding of how inhibition of GSK3 contributes to the therapeutic effects of lithium should allow for identification of more specific targets for future drug development. It may also provide a framework for the understanding of how lithium effects overlap with those of other drugs such as ketamine and antipsychotics, which also inhibit brain GSK3.

Schizophrenia Hypothesis: Autonomic Nervous System Dysregulation of Fetal and Adult Immune Tolerance

The autonomic nervous system can control immune cell activation via both sympathetic adrenergic and parasympathetic cholinergic nerve release of norepinephrine and acetylcholine. The hypothesis put forward in this paper suggests that autonomic nervous system dysfunction leads to dysregulation of immune tolerance mechanisms in brain-resident and peripheral immune cells leading to excessive production of pro-inflammatory cytokines such as Tumor Necrosis Factor alpha (TNF-α). Inactivation of Glycogen Synthase Kinase-3β (GSK3β) is a process that takes place in macrophages and microglia when a toll-like receptor 4 (TLR4) ligand binds to the TLR4 receptor. When Damage-Associated Molecular Patterns (DAMPS) and Pathogen-Associated Molecular Patterns (PAMPS) bind to TLR4s, the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway should be activated, leading to inactivation of GSK3β. This switches the macrophage from producing pro-inflammatory cytokines to anti-inflammatory cytokines. Acetylcholine activation of the α7 subunit of the nicotinic acetylcholine receptor (α7 nAChR) on the cell surface of immune cells leads to PI3K/Akt pathway activation and can control immune cell polarization. Dysregulation of this pathway due to dysfunction of the prenatal autonomic nervous system could lead to impaired fetal immune tolerance mechanisms and a greater vulnerability to Maternal Immune Activation (MIA) resulting in neurodevelopmental abnormalities. It could also lead to the adult schizophrenia patient’s immune system being more vulnerable to chronic stress-induced DAMP release. If a schizophrenia patient experiences chronic stress, an increased production of pro-inflammatory cytokines such as TNF-α could cause significant damage. TNF-α could increase the permeability of the intestinal and blood brain barrier, resulting in lipopolysaccharide (LPS) and TNF-α translocation to the brain and consequent increases in glutamate release. MIA has been found to reduce Glutamic Acid Decarboxylase mRNA expression, resulting in reduced Gamma-aminobutyric acid (GABA) synthesis, which combined with an increase of glutamate release could result in an imbalance of glutamate and GABA neurotransmitters. Schizophrenia could be a “two-hit” illness comprised of a genetic “hit” of autonomic nervous system dysfunction and an environmental hit of MIA. This combination of factors could lead to neurotransmitter imbalance and the development of psychotic symptoms.

Premise and peril of Wnt signaling activation through GSK-3β inhibition

Wnt signaling pathways have been extensively studied in the context of several diseases, including cancer, coronary artery disease, and age-related disorders. β-Catenin plays a central role in the most studied Wnt pathways, the Wnt/β-catenin signaling pathway, commonly referred to as the canonical Wnt signaling pathway. β-catenin is a substrate of glycogen synthase kinase 3β (GSK-3β), and the phosphorylated β-catenin by GSK-3β can be degraded by the proteasome through ubiquitination. Thus, GSK-3β inhibitors have become a widely used chemical biology tool to study the canonical Wnt signaling pathway. Among the varied GSK-3β inhibitors, a compound known as CHIR-99021 is one of the most widely used. Although these inhibitors contribute greatly to our understanding of the canonical Wnt pathway, certain pitfalls associated with such an approach may have been overlooked. In many published studies, micromolar concentrations of CHIR-99021 are used to activate the canonical Wnt pathway. Although CHIR-99021 is a specific GSK-3β inhibitor, it specifically inhibits the kinase at the nanomolar level. Therefore, caution is required when micromolar levels of CHIR-99021 are used for the purpose of activating the canonical Wnt signaling pathway.

Targeting the coronavirus nucleocapsid protein through GSK-3 inhibition

COVID-19 is taking a major toll on personal health, healthcare systems, and the global economy. With three betacoronavirus epidemics in less than 20 y, there is an urgent need for therapies to combat new and existing coronavirus outbreaks. Our analysis of clinical data from over 300,000 patients in three major health systems demonstrates a 50% reduced risk of COVID-19 in patients taking lithium, a direct inhibitor of glycogen synthase kinase-3 (GSK-3). We further show that GSK-3 is essential for phosphorylation of the SARS-CoV-2 nucleocapsid protein and that GSK-3 inhibition blocks SARS-CoV-2 infection in human lung epithelial cells. These findings suggest an antiviral strategy for COVID-19 and new coronaviruses that may arise in the future.

The coronaviruses responsible for severe acute respiratory syndrome (SARS-CoV), COVID-19 (SARS-CoV-2), Middle East respiratory syndrome-CoV, and other coronavirus infections express a nucleocapsid protein (N) that is essential for viral replication, transcription, and virion assembly. Phosphorylation of N from SARS-CoV by glycogen synthase kinase 3 (GSK-3) is required for its function and inhibition of GSK-3 with lithium impairs N phosphorylation, viral transcription, and replication. Here we report that the SARS-CoV-2 N protein contains GSK-3 consensus sequences and that this motif is conserved in diverse coronaviruses, raising the possibility that SARS-CoV-2 may be sensitive to GSK-3 inhibitors, including lithium. We conducted a retrospective analysis of lithium use in patients from three major health systems who were PCR-tested for SARS-CoV-2. We found that patients taking lithium have a significantly reduced risk of COVID-19 (odds ratio = 0.51 [0.35–0.74], P = 0.005). We also show that the SARS-CoV-2 N protein is phosphorylated by GSK-3. Knockout of GSK3A and GSK3B demonstrates that GSK-3 is essential for N phosphorylation. Alternative GSK-3 inhibitors block N phosphorylation and impair replication in SARS-CoV-2 infected lung epithelial cells in a cell-type–dependent manner. Targeting GSK-3 may therefore provide an approach to treat COVID-19 and future coronavirus outbreaks.

Targeting the Coronavirus Nucleocapsid Protein through GSK-3 Inhibition

The coronaviruses responsible for severe acute respiratory syndrome (SARS-CoV), COVID-19 (SARS-CoV-2), Middle East respiratory syndrome (MERS-CoV), and other coronavirus infections express a nucleocapsid protein (N) that is essential for viral replication, transcription, and virion assembly. Phosphorylation of N from SARS-CoV by glycogen synthase kinase 3 (GSK-3) is required for its function and inhibition of GSK-3 with lithium impairs N phosphorylation, viral transcription, and replication. Here we report that the SARS-CoV-2 N protein contains GSK-3 consensus sequences and that this motif is conserved in diverse coronaviruses, raising the possibility that SARS-CoV-2 may be sensitive to GSK-3 inhibitors including lithium. We conducted a retrospective analysis of lithium use in patients from three major health systems who were PCR tested for SARS-CoV-2. We found that patients taking lithium have a significantly reduced risk of COVID-19 (odds ratio = 0.51 [0.35 - 0.74], p = 0.005). We also show that the SARS-CoV-2 N protein is phosphorylated by GSK-3. Knockout of GSK3A and GSK3B demonstrates that GSK-3 is essential for N phosphorylation. Alternative GSK-3 inhibitors block N phosphorylation and impair replication in SARS-CoV-2 infected lung epithelial cells in a cell-type dependent manner. Targeting GSK-3 may therefore provide a new approach to treat COVID-19 and future coronavirus outbreaks.

Significance

COVID-19 is taking a major toll on personal health, healthcare systems, and the global economy. With three betacoronavirus epidemics in less than 20 years, there is an urgent need for therapies to combat new and existing coronavirus outbreaks. Our analysis of clinical data from over 300,000 patients in three major health systems demonstrates a 50% reduced risk of COVID-19 in patients taking lithium, a direct inhibitor of glycogen synthase kinase-3 (GSK-3). We further show that GSK-3 is essential for phosphorylation of the SARS-CoV-2 nucleocapsid protein and that GSK-3 inhibition blocks SARS-CoV-2 infection in human lung epithelial cells. These findings suggest an antiviral strategy for COVID-19 and new coronaviruses that may arise in the future.

Posttranslational modifications & lithium's therapeutic effect-Potential biomarkers for clinical responses in psychiatric & neurodegenerative disorders

Several neurodegenerative diseases and neuropsychiatric disorders display aberrant posttranslational modifications (PTMs) of one, or many, proteins. Lithium treatment has been used for mood stabilization for many decades, and is highly effective for large subsets of patients with diverse neurological conditions. However, the differential effectiveness and mode of action are not fully understood. In recent years, studies have shown that lithium alters several protein PTMs, altering their function, and consequently neuronal physiology. The impetus for this review is to outline the links between lithium's therapeutic mode of action and PTM homeostasis. We first provide an overview of the principal PTMs affected by lithium. We then describe several neuropsychiatric disorders in which PTMs have been implicated as pathogenic. For each of these conditions, we discuss lithium's clinical use and explore the putative mechanism of how it restores PTM homeostasis, and thereby cellular physiology. Evidence suggests that determining specific PTM patterns could be a promising strategy to develop biomarkers for disease and lithium responsiveness.

Lithium and Therapeutic Targeting of GSK-3

Lithium salts have been in the therapeutic toolbox for better or worse since the 19th century, with purported benefit in gout, hangover, insomnia, and early suggestions that lithium improved psychiatric disorders. However, the remarkable effects of lithium reported by John Cade and subsequently by Mogens Schou revolutionized the treatment of bipolar disorder. The known molecular targets of lithium are surprisingly few and include the signaling kinase glycogen synthase kinase-3 (GSK-3), a group of structurally related phosphomonoesterases that includes inositol monophosphatases, and phosphoglucomutase. Here we present a brief history of the therapeutic uses of lithium and then focus on GSK-3 as a therapeutic target in diverse diseases, including bipolar disorder, cancer, and coronavirus infections.

Advances toward precision medicine for bipolar disorder: mechanisms & molecules

Given its chronicity, contribution to disability and morbidity, and prevalence of more than 2%, the effective treatment, and prevention of bipolar disorder represents an area of significant unmet medical need. While more than half a century has passed since the introduction of lithium into widespread use at the birth of modern psychopharmacology, that medication remains a mainstay for the acute treatment and prevention of recurrent mania/hypomania and depression that characterize bipolar disorder. However, the continued limited understanding of how lithium modulates affective behavior and lack of validated cellular and animal models have resulted in obstacles to discovering more effective mood stabilizers with fewer adverse side effects. In particular, while there has been progress in developing new pharmacotherapy for mania, developing effective treatments for acute bipolar depression remain inadequate. Recent large-scale human genetic studies have confirmed the complex, polygenic nature of the risk architecture of bipolar disorder, and its overlap with other major neuropsychiatric disorders. Such discoveries have begun to shed light on the pathophysiology of bipolar disorder. Coupled with broader advances in human neurobiology, neuropharmacology, noninvasive neuromodulation, and clinical trial design, we can envision novel therapeutic strategies informed by defined molecular mechanisms and neural circuits and targeted to the root cause of the pathophysiology. Here, we review recent advances toward the goal of better treatments for bipolar disorder, and we outline major challenges for the field of translational neuroscience that necessitate continued focus on fundamental research and discovery.

Is There Justification to Treat Neurodegenerative Disorders by Repurposing Drugs? The Case of Alzheimer's Disease, Lithium, and Autophagy

Lithium is the prototype mood-stabilizer used for acute and long-term treatment of bipolar disorder. Cumulated translational research of lithium indicated the drug's neuroprotective characteristics and, thereby, has raised the option of repurposing it as a drug for neurodegenerative diseases. Lithium's neuroprotective properties rely on its modulation of homeostatic mechanisms such as inflammation, mitochondrial function, oxidative stress, autophagy, and apoptosis. This myriad of intracellular responses are, possibly, consequences of the drug's inhibition of the enzymes inositol-monophosphatase (IMPase) and glycogen-synthase-kinase (GSK)-3. Here we review lithium's neurobiological properties as evidenced by its neurotrophic and neuroprotective properties, as well as translational studies in cells in culture, in animal models of Alzheimer's disease (AD) and in patients, discussing the rationale for the drug's use in the treatment of AD.

Conditional GSK3β deletion in parvalbumin-expressing interneurons potentiates excitatory synaptic function and learning in adult mice

Glycogen synthase kinase 3β (GSK3β) has gained interest regarding its involvement in psychiatric and neurodegenerative disorders. Recently GSK3 inhibitors were highlighted as promising rescuers of cognitive impairments for a gamut of CNS disorders. Growing evidence supports that fast-spiking parvalbumin (PV) interneurons are critical regulators of cortical computation. Albeit, how excitatory receptors on PV interneurons are regulated and how this affects cognitive function remains unknown. To address these questions, we have generated a novel triple-transgenic conditional mouse with GSK3β genetically deleted from PV interneurons. PV-GSK3β^-/- resulted in increased excitability and augmented excitatory synaptic strength in prefrontal PV interneurons. More importantly, these synaptic changes are correlated with accelerated learning with no changes in locomotion and sociability. Our study, for the first time, examined how GSK3β activity affects learning capability via regulation of PV interneurons. This study provides a novel insight into how GSK3β may contribute to disorders afflicted by cognitive deficits.

Exendin-4 Attenuates Remodeling in the Remote Myocardium of Rats After an Acute Myocardial Infarction by Activating β-Arrestin-2, Protein Phosphatase 2A, and Glycogen Synthase Kinase-3 and Inhibiting β-Catenin

PURPOSE

This study tested if the protective anti-remodeling effect of GLP-1 agonist Exendin-4 after an acute myocardial infarction (MI) in rats involves inhibition of the Wnt1/β-catenin signaling pathway.

METHODS

Rats were divided into sham, sham + Exendin-4 (10 μg/day, i.p), MI, and MI + Exendin-4. MI was introduced to rats by permanent left anterior descending coronary artery (LAD) ligation.

RESULTS

On day 7 post-infraction, MI rats showed LV dysfunction with higher serum levels of cardiac markers. Their remote myocardia showed increased mRNA and protein levels of collagen I/III with higher levels of reactive oxygen species (ROS) and inflammatory cytokines, as well as protein levels of Wnt1, phospho-Akt, transforming growth factor (TGF-β1), Smad, phospho-Smad3, α-SMA, caspase-3, and Bax. They also showed higher protein levels of phospho-glycogen synthase kinase-3β (p-GSK3β), as well as total, phosphorylated, and nuclear β-catenin with a concomitant decrease in the levels of cyclic adenosine monophosphate (cAMP), mRNA of manganese superoxide dismutase (MnSOD), and protein levels of Bcl-2, β-arrestin-2, and protein phosphatase-2 (PP2A). Administration of Exendin-4 to MI rats reduced the infarct size and reversed the aforementioned signaling molecules without altering protein levels of TGF-1β and Wnt1 or Akt activation. Interestingly, Exendin-4 increased mRNA levels of MnSOD, protein levels of β-arrestin-2 and PP2A, and β-catenin phosphorylation but reduced the phosphorylation of GSK3β and Smad3, and total β-catenin levels in the LV of control rats.

CONCLUSION

Exendin-4 inhibits the remodeling in the remote myocardium of rats following acute MI by attenuating β-catenin activation and activating β-arrestin-2, PP2A, and GSK3β. Graphical Abstract A graphical abstract that illustrates the mechanisms by which Exendin-4 inhibits cardiac remodeling in remote myocardium of left ventricle MI-induced rats. Mechanisms are assumed to occur in the cardiomyocytes and/or other resident cells such as fibroblast. Β-catenin activation and nuclear translocation are associated with increased synthesis of inflammatory cytokines and transforming growth factor β-1 (TGF-β1). GSK3β is inhibited by phosphorylation at Ser⁹. Under normal conditions, β-catenin is degraded in the cytoplasm by the active GSK3β-dependent degradation complex (un-phosphorylated) which usually phosphorylates β-catenin at Ser^33/37/Thr⁴¹. After MI, TGF-β1, and Wnt 1 levels are significantly increased, the overproduction of Wnt1 induces β-catenin stabilization and nuclear translocation through increasing the phosphorylation of disheveled (DVL) protein which in turn phosphorylates and inhibits GSK3β. TGF-β1 stimulates the phosphorylation of Smad-3 and subsequent nuclear translocation to activate the transcription of collage 1/III and α-smooth muscle actin (α-SMA). Besides, TGF-β1 stabilizes cytoplasmic β-catenin levels indirectly by phosphorylation of Akt at Thr³⁰⁸-induced inhibition of GSK3β by increasing phosphorylation of Ser⁹. Exendin-4, and possibly through G protein-coupled receptors (GPCRs), increases levels of cAMP and upregulates β-arrestin-2 levels. Both can result in a positive inotropic effect. Besides, β-arrestin-2 can stimulate PP2A to dephosphorylation Smad3 (inhibition) and GSK3β (activation), thus reduces fibrosis and prevents the activation of β-catenin and collagen deposition.

Control of neuronal excitability by GSK-3beta: Epilepsy and beyond

Glycogen synthase kinase 3beta (GSK-3β) is an enzyme with a variety of cellular functions in addition to the regulation of glycogen metabolism. In the central nervous system, different intracellular signaling pathways converge on GSK-3β through a cascade of phosphorylation events that ultimately control a broad range of neuronal functions in the development and adulthood. In mice, genetically removing or increasing GSK-3β cause distinct functional and structural neuronal phenotypes and consequently affect cognition. Precise control of GSK-3β activity is important for such processes as neuronal migration, development of neuronal morphology, synaptic plasticity, excitability, and gene expression. Altered GSK-3β activity contributes to aberrant plasticity within neuronal circuits leading to neurological, psychiatric disorders, and neurodegenerative diseases. Therapeutically targeting GSK-3β can restore the aberrant plasticity of neuronal networks at least in animal models of these diseases. Although the complete repertoire of GSK-3β neuronal substrates has not been defined, emerging evidence shows that different ion channels and their accessory proteins controlling excitability, neurotransmitter release, and synaptic transmission are regulated by GSK-3β, thereby supporting mechanisms of synaptic plasticity in cognition. Dysregulation of ion channel function by defective GSK-3β activity sustains abnormal excitability in the development of epilepsy and other GSK-3β-linked human diseases.

Glycogen synthase kinase-3 signaling in cellular and behavioral responses to psychostimulant drugs

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase implicated in numerous physiological processes and cellular functions through its ability to regulate the function of many proteins, including transcription factors and structural proteins. GSK-3β has been demonstrated to function as a regulator of multiple behavioral processes induced by drugs of abuse, particularly psychostimulant drugs. In this review, we provide an overview of the regulation of GSK-3β activity produced by psychostimulants, and the role of GSK-3β signaling in psychostimulant-induced behaviors including drug reward, associative learning and memory which play a role in the maintenance of drug-seeking. Evidence supports the conclusion that GSK-3β is an important component of the actions of psychostimulant drugs and that GSK-3β is a valid target for developing novel therapeutics. Additional studies are required to examine the role of GSK-3β in distinct cell types within the mesolimbic and memory circuits to further elucidate the mechanisms related to the acquisition, consolidation, and recall of drug-related memories, and potentially countering neuroadaptations that reinforce drug-seeking behaviors that maintain drug dependence.

β-Arrestin2 is a critical component of the GPCR-eNOS signalosome

Endothelial cell nitric oxide (NO) synthase (eNOS), the enzyme responsible for synthesis of NO in endothelial cells, is regulated by complex posttranslational mechanisms. Sinusoidal portal hypertension, a disorder characterized by liver sinusoidal endothelial cell (SEC) injury with resultant reduced eNOS activity and NO production within the liver, has been associated with defects in eNOS protein-protein interactions and posttranslational modifications. We and others have previously identified novel eNOS interactors, including G protein-coupled receptor (GPCR) kinase interactor 1 (GIT1), which we found to play an unexpected stimulatory role in GPCR-mediated eNOS signaling. Here we report that β-arrestin 2 (β-Arr2), a canonical GPCR signaling partner, localizes in SECs with eNOS in a GIT1/eNOS/NO signaling module. Most importantly, we show that β-Arr2 stimulates eNOS activity, and that β-Arr2 expression is reduced and formation of the GIT1/eNOS/NO signaling module is interrupted during liver injury. In β-Arr2-deficient mice, bile duct ligation injury (BDL) led to significantly reduced eNOS activity and to a dramatic increase in portal hypertension compared to BDL in wild-type mice. Overexpression of β-Arr2 in injured or β-Arr2-deficient SECs rescued eNOS function by increasing eNOS complex formation and NO production. We also found that β-Arr2-mediated GIT1/eNOS complex formation is dependent on Erk1/2 and Src, two kinases known to interact with and be activated by β-Arr2 in response to GCPR activation. Our data emphasize that β-Arr2 is an integral component of the GIT1/eNOS/NO signaling pathway and have implications for the pathogenesis of sinusoidal portal hypertension.

GSK3β: A Master Player in Depressive Disorder Pathogenesis and Treatment Responsiveness

Glycogen synthase kinase 3β (GSK3β), originally described as a negative regulator of glycogen synthesis, is a molecular hub linking numerous signaling pathways in a cell. Specific GSK3β inhibitors have anti-depressant effects and reduce depressive-like behavior in animal models of depression. Therefore, GSK3β is suggested to be engaged in the pathogenesis of major depressive disorder, and to be a target and/or modifier of anti-depressants’ action. In this review, we discuss abnormalities in the activity of GSK3β and its upstream regulators in different brain regions during depressive episodes. Additionally, putative role(s) of GSK3β in the pathogenesis of depression and the influence of anti-depressants on GSK3β activity are discussed.

Putative Mechanisms of Action and Clinical Use of Lithium in Children and Adolescents: A Critical Review

Background:

Lithium is a first-line treatment for bipolar disorder in adults, but its mechanism of action is still far from clear. Furthermore, evidences of its use in pediatric populations are sparse, not only for bipolar disorders, but also for other possible indications.

Objectives:

To provide a synthesis of published data on the possible mechanisms of action of lithium, as well as on its use in pediatric samples, including pharmacokinetics, efficacy, and safety data.

Methods:

Clinical trials in pediatric samples with at least one standardized measure of efficacy/effectiveness were included in this review. We considered: i) randomized and open label trials, ii) combination studies iii) augmentation studies iv) case series including at least 5 patients.

Results:

Different and non-alternative mechanisms of action can explain the clinical efficacy of lithium. Clinical studies in pediatric samples suggest that lithium is effective in managing manic symptoms/episodes of bipolar disorder, both in the acute phase and as maintenance strategy. Efficacy on depressive symptoms/phases of bipolar disorder is much less clear, while studies do not support its use in unipolar depression and severe mood dysregulation. Conversely, it may be effective on aggression in the context of conduct disorder. Other possible indications, with limited published evidence, are the acute attacks in Kleine-Levin syndrome, behavioral symptoms of X-fragile syndrome, and the management of clozapine- or chemotherapy- induced neutropenia. Generally, lithium resulted relatively safe.

Conclusions:

Lithium seems an effective and well-tolerated medication in pediatric bipolar disorder and aggression, while further evidences are needed for other clinical indications.

Adult hippocampal neurogenesis is not necessary for the response to lithium in the forced swim test

Chronic lithium treatment stimulates adult hippocampal neurogenesis, but whether increased neurogenesis contributes to its therapeutic mechanism remains unclear. We use a genetic model of neural progenitor cell (NPC) ablation to test whether a lithium-sensitive behavior requires hippocampal neurogenesis. NPC-ablated mice were treated with lithium and assessed in the forced swim test (FST). Lithium reduced time immobile in the FST in NPC-ablated and control mice but had no effect on activity in the open field, a control for the locomotion-based FST. These findings show that hippocampal NPCs that proliferate in response to chronic lithium are not necessary for the behavioral response to lithium in the FST. We further show that 4-6 week old immature hippocampal neurons are not required for this response. These data suggest that increased hippocampal neurogenesis does not contribute to the response to lithium in the forced swim test and may not be an essential component of its therapeutic mechanism.

Dopamine: Functions, Signaling, and Association with Neurological Diseases

The dopaminergic system plays important roles in neuromodulation, such as motor control, motivation, reward, cognitive function, maternal, and reproductive behaviors. Dopamine is a neurotransmitter, synthesized in both central nervous system and the periphery, that exerts its actions upon binding to G protein-coupled receptors. Dopamine receptors are widely expressed in the body and function in both the peripheral and the central nervous systems. Dopaminergic signaling pathways are crucial to the maintenance of physiological processes and an unbalanced activity may lead to dysfunctions that are related to neurodegenerative diseases. Unveiling the neurobiology and the molecular mechanisms that underlie these illnesses may contribute to the development of new therapies that could promote a better quality of life for patients worldwide. In this review, we summarize the aspects of dopamine as a catecholaminergic neurotransmitter and discuss dopamine signaling pathways elicited through dopamine receptor activation in normal brain function. Furthermore, we describe the potential involvement of these signaling pathways in evoking the onset and progression of some diseases in the nervous system, such as Parkinson's, Schizophrenia, Huntington's, Attention Deficit and Hyperactivity Disorder, and Addiction. A brief description of new dopaminergic drugs recently approved and under development treatments for these ailments is also provided.

NO-sGC-cGMP signaling influence the anxiolytic like effect of lithium in mice in light and dark box and elevated plus maze

Glutamate is an excitatory neurotransmitter implicated in the pathogenesis of psychiatric disorders. Glutamate results in the activation of an enzyme called glycogen synthase kinase-3 (GSK-3) acting through N-methyl-d-aspartate (NMDA) receptors. Impaired expression of GSK-3 affects behavior and neurochemicals level in the brain responsible for the pathogenesis of mood disorders. It has been reported that lithium acts as an inhibitor of GSK-3 and inhibit the enzyme GSK-3 in an uncompetitive manner. In the present study, anxiolytic like effect of lithium in mice is investigated through light and dark box (LDB) and elevated plus maze (EPM). Lithium (50, 100 and 200 mg/kg, i.p.) was administered to the mice to determine the anxiety related behavior. Results obtained suggests that the administration of lithium (100 mg/kg, i.p.) reversed the anxiety related behavior of mice and decreased the levels of glutamate and nitrite as compared to control. Glutamate acting through the NMDA receptor has been found to regulate the expression of enzyme neuronal nitric oxide synthase (nNOS), which is responsible for the release of nitric oxide (NO), suggesting a possible link between NO and GSK-3 also. Therefore, to determine the possible interaction with NO, sub-effective dose of lithium was administered in combination with NO donor i.e. l-Arginine (50 mg/kg, i.p.), NOS and soluble guanylate cyclase (sGC) inhibitor i.e. methylene blue (1 mg/kg, i.p.) and phosphodiesterase inhibitor i.e. sildenafil (1 mg/kg, i.p.). The results obtained demonstrated that the anxiolytic like effect of lithium was abolished by the pretreatment with NO donor and potentiated by the pretreatment with NOS inhibitor. Therefore, it is suggested that NO signaling pathway influence the anxiolytic like activity of lithium in mice, further suggesting the link between the GSK-3 and NO signaling in the regulation of anxiety related behavior.

Targeting GSK3 signaling as a potential therapy of neurodegenerative diseases and aging

INTRODUCTION

Glycogen synthase kinase 3 (GSK3) is at the center of cellular signaling and controls various aspects of brain functions, including development of the nervous system, neuronal plasticity and onset of neurodegenerative disorders. Areas covered: In this review, recent efforts in elucidating the roles of GSK3 in neuronal plasticity and development of brain pathologies; Alzheimer's and Parkinson's disease, schizophrenia, and age-related neurodegeneration are described. The effect of microglia and astrocytes on development of the pathological states is also discussed. Expert opinion: GSK3β and its signaling pathway partners hold great promise as therapeutic target(s) for a multitude of neurological disorders. Activity of the kinase is often elevated in brain disorders. However, due to the wide range of GSK3 cellular targets, global inhibition of the kinase leads to severe side-effects and GSK3 inhibitors rarely reach Phase-2 clinical trials. Thus, a selective modulation of a specific cellular pool of GSK3 or specific down- or upstream partners of the kinase might provide more efficient anti-neurodegenerative therapies.

Molecular Mechanisms of Lithium Action: Switching the Light on Multiple Targets for Dementia Using Animal Models

Lithium has long been used for the treatment of psychiatric disorders, due to its robust beneficial effect as a mood stabilizing drug. Lithium’s effectiveness for improving neurological function is therefore well-described, stimulating the investigation of its potential use in several neurodegenerative conditions including Alzheimer’s (AD), Parkinson’s (PD) and Huntington’s (HD) diseases. A narrow therapeutic window for these effects, however, has led to concerted efforts to understand the molecular mechanisms of lithium action in the brain, in order to develop more selective treatments that harness its neuroprotective potential whilst limiting contraindications. Animal models have proven pivotal in these studies, with lithium displaying advantageous effects on behavior across species, including worms (C. elegans), zebrafish (Danio rerio), fruit flies (Drosophila melanogaster) and rodents. Due to their susceptibility to genetic manipulation, functional genomic analyses in these model organisms have provided evidence for the main molecular determinants of lithium action, including inhibition of inositol monophosphatase (IMPA) and glycogen synthase kinase-3 (GSK-3). Accumulating pre-clinical evidence has indeed provided a basis for research into the therapeutic use of lithium for the treatment of dementia, an area of medical priority due to its increasing global impact and lack of disease-modifying drugs. Although lithium has been extensively described to prevent AD-associated amyloid and tau pathologies, this review article will focus on generic mechanisms by which lithium preserves neuronal function and improves memory in animal models of dementia. Of these, evidence from worms, flies and mice points to GSK-3 as the most robust mediator of lithium’s neuro-protective effect, but it’s interaction with downstream pathways, including Wnt/β-catenin, CREB/brain-derived neurotrophic factor (BDNF), nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and toll-like receptor 4 (TLR4)/nuclear factor-κB (NFκB), have identified multiple targets for development of drugs which harness lithium’s neurogenic, cytoprotective, synaptic maintenance, anti-oxidant, anti-inflammatory and protein homeostasis properties, in addition to more potent and selective GSK-3 inhibitors. Lithium, therefore, has advantages as a multi-functional therapy to combat the complex molecular pathology of dementia. Animal studies will be vital, however, for comparative analyses to determine which of these defense mechanisms are most required to slow-down cognitive decline in dementia, and whether combination therapies can synergize systems to exploit lithium’s neuro-protective power while avoiding deleterious toxicity.

G Protein-Coupled Receptor Signaling Through β-Arrestin-Dependent Mechanisms

β-arrestin1 (or arrestin2) and β-arrestin2 (or arrestin3) are ubiquitously expressed cytosolic adaptor proteins that were originally discovered for their inhibitory role in G protein-coupled receptor (GPCR) signaling through heterotrimeric G proteins. However, further biochemical characterization revealed that β-arrestins do not just "block" the activated GPCRs, but trigger endocytosis and kinase activation leading to specific signaling pathways that can be localized on endosomes. The signaling pathways initiated by β-arrestins were also found to be independent of G protein activation by GPCRs. The discovery of ligands that blocked G protein activation but promoted β-arrestin binding, or vice-versa, suggested the exciting possibility of selectively activating intracellular signaling pathways. In addition, it is becoming increasingly evident that β-arrestin-dependent signaling is extremely diverse and provokes distinct cellular responses through different GPCRs even when the same effector kinase is involved. In this review, we summarize various signaling pathways mediated by β-arrestins and highlight the physiologic effects of β-arrestin-dependent signaling.

Heat shock protein A12A encodes a novel prosurvival pathway during ischaemic stroke

Heat shock protein A12A (HSPA12A) is a newly discovered member of the Hsp70 family. The biological characteristics and functional roles of HSPA12A are poorly understood. This study investigated the effects of HSPA12A on ischaemic stroke in mice. Ischaemic stroke was induced by left middle cerebral artery occlusion for 1 h followed by blood reperfusion. We observed that HSPA12A was highly expressed in brain neurons, and neuronal HSPA12A expression was downregulated by ischaemic stroke and stroke-associated risk factors (aging, obesity and hyperglycaemia). To investigate the functional requirement of HSPA12A in protecting ischaemic brain injury, HSPA12A knockout mice (Hspa12a^-/-) were generated. Hspa12a^-/- mice exhibited an enlarged infarct volume and aggravated neurological deficits compared to their wild-type (WT) littermates after stroke. These aggravations in Hspa12a^-/- mice were accompanied by more apoptosis and severer hippocampal morphological abnormalities in ischaemic hemispheres. Long-term examination revealed impaired motor function recovery and neurogenesis in stroke-affected Hspa12a^-/- mice compared to stroke-affected WT controls. Significant reduced activation of GSK-3β/mTOR/p70S6K signalling was also observed in ischaemic hemispheres of Hspa12a^-/- mice compared to WT controls. Administration with lithium (non-selective GSK-3β inhibitor) activated GSK-3β/mTOR/p70S6K signalling in stroke-affected Hspa12a^-/- mice. Notably, lithium administration attenuated the HSPA12A deficiency-induced aggravation in infarct size, neurological deficits and neuronal death in Hspa12a^-/- mice after stroke. Altogether, the findings suggest that HSPA12A expression encodes a critical novel prosurvival pathway during ischaemic stroke. We identified HSPA12A as a novel neuroprotective target for stroke patients.

Animal models for bipolar disorder: from bedside to the cage

Bipolar disorder is characterized by recurrent manic and depressive episodes. Patients suffering from this disorder experience dramatic mood swings with a wide variety of typical behavioral facets, affecting overall activity, energy, sexual behavior, sense of self, self-esteem, circadian rhythm, cognition, and increased risk for suicide. Effective treatment options are limited and diagnosis can be complicated. To overcome these obstacles, a better understanding of the neurobiology underlying bipolar disorder is needed. Animal models can be useful tools in understanding brain mechanisms associated with certain behavior. The following review discusses several pathological aspects of humans suffering from bipolar disorder and compares these findings with insights obtained from several animal models mimicking diverse facets of its symptomatology. Various sections of the review concentrate on specific topics that are relevant in human patients, namely circadian rhythms, neurotransmitters, focusing on the dopaminergic system, stressful environment, and the immune system. We then explain how these areas have been manipulated to create animal models for the disorder. Even though several approaches have been conducted, there is still a lack of adequate animal models for bipolar disorder. Specifically, most animal models mimic only mania or depression and only a few include the cyclical nature of the human condition. Future studies could therefore focus on modeling both episodes in the same animal model to also have the possibility to investigate the switch from mania-like behavior to depressive-like behavior and vice versa. The use of viral tools and a focus on circadian rhythms and the immune system might make the creation of such animal models possible.

Precision medicine for suicidality: from universality to subtypes and personalization

Suicide remains a clear, present and increasing public health problem, despite being a potentially preventable tragedy. Its incidence is particularly high in people with overt or un(der)diagnosed psychiatric disorders. Objective and precise identification of individuals at risk, ways of monitoring response to treatments and novel preventive therapeutics need to be discovered, employed and widely deployed. We sought to investigate whether blood gene expression biomarkers for suicide (that is, a 'liquid biopsy' approach) can be identified that are more universal in nature, working across psychiatric diagnoses and genders, using larger cohorts than in previous studies. Such markers may reflect and/or be a proxy for the core biology of suicide. We were successful in this endeavor, using a comprehensive stepwise approach, leading to a wealth of findings. Steps 1, 2 and 3 were discovery, prioritization and validation for tracking suicidality, resulting in a Top Dozen list of candidate biomarkers comprising the top biomarkers from each step, as well as a larger list of 148 candidate biomarkers that survived Bonferroni correction in the validation step. Step 4 was testing the Top Dozen list and Bonferroni biomarker list for predictive ability for suicidal ideation (SI) and for future hospitalizations for suicidality in independent cohorts, leading to the identification of completely novel predictive biomarkers (such as CLN5 and AK2), as well as reinforcement of ours and others previous findings in the field (such as SLC4A4 and SKA2). Additionally, we examined whether subtypes of suicidality can be identified based on mental state at the time of high SI and identified four potential subtypes: high anxiety, low mood, combined and non-affective (psychotic). Such subtypes may delineate groups of individuals that are more homogenous in terms of suicidality biology and behavior. We also studied a more personalized approach, by psychiatric diagnosis and gender, with a focus on bipolar males, the highest risk group. Such a personalized approach may be more sensitive to gender differences and to the impact of psychiatric co-morbidities and medications. We compared testing the universal biomarkers in everybody versus testing by subtypes versus personalized by gender and diagnosis, and show that the subtype and personalized approaches permit enhanced precision of predictions for different universal biomarkers. In particular, LHFP appears to be a strong predictor for suicidality in males with depression. We also directly examined whether biomarkers discovered using male bipolars only are better predictors in a male bipolar independent cohort than universal biomarkers and show evidence for a possible advantage of personalization. We identified completely novel biomarkers (such as SPTBN1 and C7orf73), and reinforced previously known biomarkers (such as PTEN and SAT1). For diagnostic ability testing purposes, we also examined as predictors phenotypic measures as apps (for suicide risk (CFI-S, Convergent Functional Information for Suicidality) and for anxiety and mood (SASS, Simplified Affective State Scale)) by themselves, as well as in combination with the top biomarkers (the combination being our a priori primary endpoint), to provide context and enhance precision of predictions. We obtained area under the curves of 90% for SI and 77% for future hospitalizations in independent cohorts. Step 5 was to look for mechanistic understanding, starting with examining evidence for the Top Dozen and Bonferroni biomarkers for involvement in other psychiatric and non-psychiatric disorders, as a mechanism for biological predisposition and vulnerability. The biomarkers we identified also provide a window towards understanding the biology of suicide, implicating biological pathways related to neurogenesis, programmed cell death and insulin signaling from the universal biomarkers, as well as mTOR signaling from the male bipolar biomarkers. In particular, HTR2A increase coupled with ARRB1 and GSK3B decreases in expression in suicidality may provide a synergistic mechanistical corrective target, as do SLC4A4 increase coupled with AHCYL1 and AHCYL2 decrease. Step 6 was to move beyond diagnostics and mechanistical risk assessment, towards providing a foundation for personalized therapeutics. Items scored positive in the CFI-S and subtypes identified by SASS in different individuals provide targets for personalized (psycho)therapy. Some individual biomarkers are targets of existing drugs used to treat mood disorders and suicidality (lithium, clozapine and omega-3 fatty acids), providing a means toward pharmacogenomics stratification of patients and monitoring of response to treatment. Such biomarkers merit evaluation in clinical trials. Bioinformatics drug repurposing analyses with the gene expression biosignatures of the Top Dozen and Bonferroni-validated universal biomarkers identified novel potential therapeutics for suicidality, such as ebselen (a lithium mimetic), piracetam (a nootropic), chlorogenic acid (a polyphenol) and metformin (an antidiabetic and possible longevity promoting drug). Finally, based on the totality of our data and of the evidence in the field to date, a convergent functional evidence score prioritizing biomarkers that have all around evidence (track suicidality, predict it, are reflective of biological predisposition and are potential drug targets) brought to the fore APOE and IL6 from among the universal biomarkers, suggesting an inflammatory/accelerated aging component that may be a targetable common denominator.

Cotinine improves visual recognition memory and decreases cortical Tau phosphorylation in the Tg6799 mice

Alzheimer's disease (AD) is associated with the progressive aggregation of hyperphosphorylated forms of the microtubule associated protein Tau in the central nervous system. Cotinine, the main metabolite of nicotine, reduced working memory deficits, synaptic loss, and amyloid β peptide aggregation into oligomers and plaques as well as inhibited the cerebral Tau kinase, glycogen synthase 3β (GSK3β) in the transgenic (Tg)6799 (5XFAD) mice. In this study, the effect of cotinine on visual recognition memory and cortical Tau phosphorylation at the GSK3β sites Serine (Ser)-396/Ser-404 and phospho-CREB were investigated in the Tg6799 and non-transgenic (NT) littermate mice. Tg mice showed short-term visual recognition memory impairment in the novel object recognition test, and higher levels of Tau phosphorylation when compared to NT mice. Cotinine significantly improved visual recognition memory performance increased CREB phosphorylation and reduced cortical Tau phosphorylation. Potential mechanisms underlying theses beneficial effects are discussed.

Wnt and GSK3 Signaling Pathways in Bipolar Disorder: Clinical and Therapeutic Implications

The neurobiology of bipolar disorder, a chronic and systemic ailment is not completely understood. The bipolar phenotype manifests in myriad ways, and psychopharmacological agents like lithium have long term beneficial effects. The enzyme glycogen synthase kinase 3 (GSK3) has come into focus, as lithium and several other mood stabilizing medications inhibit its activity. This kinase and its key upstream modulator, Wnt are dysregulated in mood disorders and there is a growing impetus to delineate the chief substrates involved in the development of these illnesses. In May 2016, a comprehensive literature search was undertaken which revealed that there is over activity of GSK3 in bipolar disorder with deleterious downstream effects like proinflammatory status, increased oxidative stress, and circadian dysregulation leading to declining neurotrophic support and enhanced apoptosis of neural elements. By developing specific GSK3 inhibitors the progressive worsening in bipolar disorder can be forestalled with improved prospects for the sufferers.

β-arrestin is critical for early shear stress-induced Akt/eNOS activation in human vascular endothelial cells

Recent evidence suggests that β-arrestins, which are involved in G protein-coupled receptors desensitization, may influence mechanotransduction. Here, we observed that nitric oxide (NO) production was abrogated in human saphenous vein endothelial cells (SVECs) transfected with siRNA against β-arrestin 1 and 2 subjected to shear stress (SS, 15 dynes/cm², 10 min). The downregulation of β-arrestins 1/2 in SVECs cells also prevented the SS-induced rise in levels of phosphorylation of Akt and endothelial nitric oxide synthase (eNOS, Serine 1177). Interestingly, immunoprecipitation revealed that β-arrestin interacts with Akt, eNOS and caveolin-1 and these interactions are not influenced by SS. Our data indicate that β-arrestins and Akt/eNOS downstream signaling are required for early SS-induced NO production in SVECs, which is consistent with the idea that β-arrestins and caveolin-1 are part of a pre-assembled complex associated with the cellular mechanotransduction machinery.

GSK-3β and MMP-9 Cooperate in the Control of Dendritic Spine Morphology

Changes in the morphology of dendritic spines are prominent during learning and in different neurological and neuropsychiatric diseases, including those in which glycogen synthase kinase-3β (GSK-3β) has been implicated. Despite much evidence of the involvement of GSK-3β in functional synaptic plasticity, it is unclear how GSK-3β controls structural synaptic plasticity (i.e., the number and shape of dendritic spines). In the present study, we used two mouse models overexpressing and lacking GSK-3β in neurons to investigate how GSK-3β affects the structural plasticity of dendritic spines. Following visualization of dendritic spines with DiI dye, we found that increasing GSK-3β activity increased the number of thin spines, whereas lacking GSK-3β increased the number of stubby spines in the dentate gyrus. Under conditions of neuronal excitation, increasing GSK-3β activity caused higher activity of extracellularly acting matrix metalloproteinase-9 (MMP-9), and MMP inhibition normalized thin spines in GSK-3β overexpressing mice. Administration of the nonspecific GSK-3β inhibitor lithium in animals with active MMP-9 and animals lacking MMP-9 revealed that GSK-3β and MMP-9 act in concert to control dendritic spine morphology. Altogether, our data demonstrate that the dysregulation of GSK-3β activity has dramatic consequences on dendritic spine morphology, implicating MMP-9 as a mediator of GSK-3β-induced synaptic alterations.

Peripheral blood gene expression profiles linked to monoamine metabolite levels in cerebrospinal fluid

The blood-brain barrier separates circulating blood from the central nervous system (CNS). The scope of this barrier is not fully understood which limits our ability to relate biological measurements from peripheral to central phenotypes. For example, it is unknown to what extent gene expression levels in peripheral blood are reflective of CNS metabolism. In this study, we examine links between central monoamine metabolite levels and whole-blood gene expression to better understand the connection between peripheral systems and the CNS. To that end, we correlated the prime monoamine metabolites in cerebrospinal fluid (CSF) with whole-genome gene expression microarray data from blood (N=240 human subjects). We additionally applied gene-enrichment analysis and weighted gene co-expression network analyses (WGCNA) to identify modules of co-expressed genes in blood that may be involved with monoamine metabolite levels in CSF. Transcript levels of two genes were significantly associated with CSF serotonin metabolite levels after Bonferroni correction for multiple testing: THAP7 (P=2.8 × 10^-8, β=0.08) and DDX6 (P=2.9 × 10^-7, β=0.07). Differentially expressed genes were significantly enriched for genes expressed in the brain tissue (P=6.0 × 10^-52). WGCNA revealed significant correlations between serotonin metabolism and hub genes with known functions in serotonin metabolism, for example, HTR2A and COMT. We conclude that gene expression levels in whole blood are associated with monoamine metabolite levels in the human CSF. Our results, including the strong enrichment of brain-expressed genes, illustrate that gene expression profiles in peripheral blood can be relevant for quantitative metabolic phenotypes in the CNS.

TCF7L2 mediates the cellular and behavioral response to chronic lithium treatment in animal models

The mechanism of lithium's therapeutic action remains obscure, hindering the discovery of safer treatments for bipolar disorder. Lithium can act as an inhibitor of the kinase GSK3α/β, which in turn negatively regulates β-catenin, a co-activator of LEF1/TCF transcription factors. However, unclear is whether therapeutic levels of lithium activate β-catenin in the brain, and whether this activation could have a therapeutic significance. To address this issue we chronically treated mice with lithium. Although the level of non-phospho-β-catenin increased in all of the brain areas examined, β-catenin translocated into cellular nuclei only in the thalamus. Similar results were obtained when thalamic and cortical neurons were treated with a therapeutically relevant concentration of lithium in vitro. We tested if TCF7L2, a member of LEF1/TCF family that is highly expressed in the thalamus, facilitated the activation of β-catenin. Silencing of Tcf7l2 in thalamic neurons prevented β-catenin from entering the nucleus, even when the cells were treated with lithium. Conversely, when Tcf7l2 was ectopically expressed in cortical neurons, β-catenin shifted to the nucleus, and lithium augmented this process. Lastly, we silenced tcf7l2 in zebrafish and exposed them to lithium for 3 days, to evaluate whether TCF7L2 is involved in the behavioral response. Lithium decreased the dark-induced activity of control zebrafish, whereas the activity of zebrafish with tcf7l2 knockdown was unaltered. We conclude that therapeutic levels of lithium activate β-catenin selectively in thalamic neurons. This effect is determined by the presence of TCF7L2, and potentially contributes to the therapeutic response.

The Role of Elements in Anxiety

Elements (bioelements) are necessary factors required for the physiological function of organisms. They are critically involved in fundamental processes of life. Extra- and intracellular message and metabolic pathway factors as well as structural components include one or many elements in their functional structure. Recent years have seen an intensification in terms of knowledge gained about the roles of elements in anxiety disorders. In this chapter we present a review of the most important current data concerning the involvement of zinc, magnesium, copper, lithium, iron, and manganese, and their deficiency, in the pathophysiology and treatment of anxiety.

Converging evidence for regulation of dopamine neurotransmission by lithium: An Editorial Highlight for 'Chronic lithium treatment rectifies maladaptive dopamine release in the nucleus accumbens'

Read the highlighted article 'Chronic lithium treatment rectifies maladaptive dopamine release in the nucleus accumbens' on page 576.

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

Protease-activated receptors PAR1 and PAR2 play an important role in the control of epithelial cell proliferation and migration. However, the survival of normal and tumor intestinal stem/progenitor cells promoted by proinflammatory mediators may be critical in oncogenesis. The glycogen synthase kinase-3β (GSK3β) pathway is overactivated in colon cancer cells and promotes their survival and drug resistance. We thus aimed to determine PAR1 and PAR2 effects on normal and tumor intestinal stem/progenitor cells and whether they involved GSK3β. First, PAR1 and PAR2 were identified in colon stem/progenitor cells by immunofluorescence. In three-dimensional cultures of murine crypt units or single tumor Caco-2 cells, PAR2 activation decreased numbers and size of normal or cancerous spheroids, and PAR2-deficient spheroids showed increased proliferation, indicating that PAR2 represses proliferation. PAR2-stimulated normal cells were more resistant to stress (serum starvation or spheroid passaging), suggesting prosurvival effects of PAR2 Accordingly, active caspase-3 was strongly increased in PAR2-deficient normal spheroids. PAR2 but not PAR1 triggered GSK3β activation through serine-9 dephosphorylation in normal and tumor cells. The PAR2-triggered GSK3β activation implicates an arrestin/PP2A/GSK3β complex that is dependent on the Rho kinase activity. Loss of PAR2 was associated with high levels of GSK3β nonactive form, strengthening the role of PAR2 in GSK3β activation. GSK3 pharmacological inhibition impaired the survival of PAR2-stimulated spheroids and serum-starved cells. Altogether our data identify PAR2/GSK3β as a novel pathway that plays a critical role in the regulation of stem/progenitor cell survival and proliferation in normal colon crypts and colon cancer.

Inositol depletion, GSK3 inhibition and bipolar disorder

Valproic acid and lithium are widely used to treat bipolar disorder, a severe illness characterized by cycles of mania and depression. However, their efficacy is limited, and treatment is often accompanied by serious side effects. The therapeutic mechanisms of these drugs are not understood, hampering the development of more effective treatments. Among the plethora of biochemical effects of the drugs, those that are common to both may be more related to therapeutic efficacy. Two common outcomes include inositol depletion and GSK3 inhibition, which have been proposed to explain the efficacy of both valproic acid and lithium. Here, we discuss the inositol depletion and GSK3 inhibition hypotheses, and introduce a unified model suggesting that inositol depletion and GSK3 inhibition are inter-related.

Antipsychotic-like effects of a neurotensin receptor type 1 agonist

Although neurotensin (NT) analogs are known to produce antipsychotic-like effects, the therapeutic possibility of a brain penetrant NTS1 agonist in treating psychiatric disorders has not been well studied. Here, we examined whether PD149163, a brain-penetrant NTS1-specific agonist, displays antipsychotic-like effects in C57BL/6J mice by investigating the effect of PD149163 on amphetamine-mediated hyperactivity and amphetamine-induced disruption of prepulse inhibition. In addition, we assessed the effect of PD149163 on glycogen synthase kinase-3 (GSK-3) activity, a downstream molecular target of antipsychotics and mood stabilizers, using phospho-specific antibodies. PD149163 (0.1 and 0.5mg/kg) inhibited amphetamine-induced hyperactivity in mice, indicating that NTS1 activation inhibits psychomotor agitation. PD149163 (0.5mg/kg) also increased prepulse inhibition, suggesting that NTS1 activation reduces prepulse inhibition deficits which often co-occur with psychosis in humans. Interestingly, PD149163 increased the inhibitory serine phosphorylation on both GSK-3α and GSK-3β in a dose- and time-dependent manner in the nucleus accumbens and medial prefrontal cortex of the mice. Moreover, PD149163 inhibited GSK-3 activity in the nucleus accumbens and medial prefrontal cortex in the presence of amphetamine. Thus, like most current antipsychotics and mood stabilizers, PD149163 inhibited GSK-3 activity in cortico-striatal circuitry. Together, our findings indicate that PD149163 may be a novel antipsychotic.

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.

β-Arrestin 2 Promotes Hepatocyte Apoptosis by Inhibiting Akt Protein

Recent studies reveal that multifunctional protein β-arrestin 2 (Arrb2) modulates cell apoptosis. Survival and various aspects of liver injury were investigated in WT and Arrb2 KO mice after bile duct ligation (BDL). We found that deficiency of Arrb2 enhances survival and attenuates hepatic injury and fibrosis. Following BDL, Arrb2-deficient mice as compared with WT controls displayed a significant reduction of hepatocyte apoptosis as demonstrated by the TUNEL assay. Following BDL, the levels of phospho-Akt and phospho-glycogen synthase kinase 3β (GSK3β) in the livers were significantly increased in Arrb2 KO compared with WT mice, although p-p38 increased in WT but not in Arrb2-deficient mice. Inhibition of GSK3β following BDL decreases hepatic apoptosis and decreased p-p38 in WT mice but not in Arrb2 KO mice. Activation of Fas receptor with Jo2 reduces phospho-Akt and increases apoptosis in WT cells and WT mice but not in Arrb2-deficient cells and Arrb2-deficient mice. Consistent with direct interaction of Arrb2 with and regulating Akt phosphorylation, the expression of a full-length or N terminus but not the C terminus of Arrb2 reduces Akt phosphorylation and coimmunoprecipates with Akt. These results reveal that the protective effect of deficiency of Arrb2 is due to loss of negative regulation of Akt due to BDL and decreased downstream GSK3β and p38 MAPK signaling pathways.

Dopamine receptors - IUPHAR Review 13

The variety of physiological functions controlled by dopamine in the brain and periphery is mediated by the D1, D2, D3, D4 and D5 dopamine GPCRs. Drugs acting on dopamine receptors are significant tools for the management of several neuropsychiatric disorders including schizophrenia, bipolar disorder, depression and Parkinson's disease. Recent investigations of dopamine receptor signalling have shown that dopamine receptors, apart from their canonical action on cAMP-mediated signalling, can regulate a myriad of cellular responses to fine-tune the expression of dopamine-associated behaviours and functions. Such signalling mechanisms may involve alternate G protein coupling or non-G protein mechanisms involving ion channels, receptor tyrosine kinases or proteins such as β-arrestins that are classically involved in GPCR desensitization. Another level of complexity is the growing appreciation of the physiological roles played by dopamine receptor heteromers. Applications of new in vivo techniques have significantly furthered the understanding of the physiological functions played by dopamine receptors. Here we provide an update of the current knowledge regarding the complex biology, signalling, physiology and pharmacology of dopamine receptors.