Lithium and synaptic plasticity

Case Studies in Neuroscience: Lack of inhibitory synaptic plasticity in the substantia nigra pars reticulata of a patient with lithium-induced tremor

Tremor is a well-known side effect from many psychiatric medications, including lithium and dopamine antagonists. In patients whose psychiatric symptoms are stabilized and only respond to certain medications, deep brain stimulation may offer relief of the consequent motor complications. We report the case of an elderly male with disabling tremor related to lithium therapy for bipolar affective disorder, who was subsequently treated with deep brain stimulation. In this patient, we obtained recordings from the substantia nigra pars reticulata and performed a high-frequency stimulation protocol that robustly elicits long-term potentiation (LTP)-like changes in patients with Parkinson's disease. We hypothesized that in this patient, who did not have Parkinson's disease, the levels of inhibitory plasticity would be much greater. However, we found an unanticipated lack of plasticity in the patient with lithium-induced tremor, compared with two de novo control patients with Parkinson's disease. This patient was successfully treated with deep brain stimulation in the vicinity of the ventral oral posterior nucleus, an area of the thalamus that receives inputs from the basal ganglia. We postulate that the lithium-induced blockade of LTP may bring about motor complications such as tremor while simultaneously contributing to the therapeutic mechanism for treating the symptoms of psychiatric disorders such as bipolar affective disorder.NEW & NOTEWORTHY Use of a dual-microelectrode technique enabled us to compare long-term potentiation (LTP)-like changes in a patient with lithium-induced tremor to that of patients with Parkinson's disease. This study corroborated the findings in rodent brain slices that chronic lithium treatment may block LTP. Whereas a deficit in LTP may underlie the therapeutic mechanism for treating psychiatric disorders such as bipolar affective disorder, it may simultaneously contribute to consequent appearance of tremor.

Gsk3 Signalling and Redox Status in Bipolar Disorder: Evidence from Lithium Efficacy

Objective. To discuss the link between glycogen synthase kinase-3 (GSK3) and the main biological alterations demonstrated in bipolar disorder (BD), with special attention to the redox status and the evidence supporting the efficacy of lithium (a GSK3 inhibitor) in the treatment of BD. Methods. A literature research on the discussed topics, using Pubmed and Google Scholar, has been conducted. Moreover, a manual selection of interesting references from the identified articles has been performed. Results. The main biological alterations of BD, pertaining to inflammation, oxidative stress, membrane ion channels, and circadian system, seem to be intertwined. The dysfunction of the GSK3 signalling pathway is involved in all the aforementioned “biological causes” of BD. In a complex scenario, it can be seen as the common denominator linking them all. Lithium inhibition of GSK3 could, at least in part, explain its positive effect on these biological dysfunctions and its superiority in terms of clinical efficacy. Conclusions. Deepening the knowledge on the molecular bases of BD is fundamental to identifying the biochemical pathways that must be targeted in order to provide patients with increasingly effective therapeutic tools against an invalidating disorder such as BD.

Loss of neuronal GSK3β reduces dendritic spine stability and attenuates excitatory synaptic transmission via β-catenin

Central nervous glycogen synthase kinase 3β (GSK3β) is implicated in a number of neuropsychiatric diseases, such as bipolar disorder, depression, schizophrenia, fragile X syndrome or anxiety disorder. Many drugs employed to treat these conditions inhibit GSK3β either directly or indirectly. We studied how conditional knockout of GSK3β affected structural synaptic plasticity. Deletion of the GSK3β gene in a subset of cortical and hippocampal neurons in adult mice led to reduced spine density. In vivo imaging revealed that this was caused by a loss of persistent spines, whereas stabilization of newly formed spines was reduced. In electrophysiological recordings, these structural alterations correlated with a considerable drop in the frequency and amplitude of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-dependent miniature excitatory postsynaptic currents. Expression of constitutively active β-catenin caused reduction in spine density and electrophysiological alterations similar to GSK3β knockout, suggesting that the effects of GSK3β knockout were mediated by the accumulation of β-catenin. In summary, changes of dendritic spines, both in quantity and in morphology, are correlates of experience-dependent synaptic plasticity; thus, these results may help explain the mechanism of action of psychotropic drugs inhibiting GSK3β.

Signal transduction pathways in the pathophysiology of bipolar disorder

Signal transduction pathways and genes associated with cellular life and death have received much attention in bipolar disorder (BPD) and provide scientists with molecular targets for understanding the biological basis of BPD. In this chapter, we describe the signal transduction pathways involved in the molecular biology of BPD and the indications for the mechanisms of disease and treatment. We discuss the BPD literature with respect to the disease itself and the effects of mood stabilizer treatment on cellular receptors, including G-protein-coupled receptors, glutamate receptors, and tyrosine receptor kinase. We also discuss the intracellular alterations observed in BPD to second messenger systems, such as cyclic adenosine monophosphate (cAMP), protein kinase A, phosphoinositide pathways, glycogen synthase kinase-3, protein kinase B, Wnt, and arachidonic acid. We describe how receptor activation and modulation of second messengers occurs, and how transcription factors are activated and altered in this disease (e.g., the transcription factors ?-catenin, cAMP response element binding protein, heat shock transcription factor-1, and activator protein-1). Abnormalities in intracellular signal transduction pathways could generate a functional discrepancy in numerous neurotransmitter systems, which may explain the varied clinical symptoms observed in BPD. The influence of mood stabilizers on transcription factors may be important in connecting the regulation of gene expression to neuroplasticity and cellular resilience.

Cytoprotective effect of lithium against spontaneous and induced apoptosis of lymphoid cell line MOLT-4

Lithium (Li) is still useful in the treatment of bipolar disorder. Cellular mechanisms of Li action are not fully understood and include some cytoprotective properties. Data concerning Li effect on the apoptotic mechanisms in cells other than neurons are fragmentary and contradictory. We have investigated anti-apoptotic activity of Li in a lymphoid derived MOLT-4 cell line. Spontaneous and camptothecin-induced apoptosis was analyzed in cells treated with 0-20 mM Li carbonate. Early apoptosis was identified as significant mitochondrial depolarization (JC-1 staining). Later stages of apoptosis were estimated with annexin V binding and by the proportion of cells containing sub-G1 amounts of DNA (PI staining). We have observed a biphasic effect of Li on the proportion of spontaneously apoptotic cells;namely, low (therapeutic) concentrations of Li had a significant effect stabilizing the mitochondrial membrane polarization, while 10 and 20mM Li increased apoptosis. The latter could be seen both as mitochondrial depolarization as well as an increased proportion of sub-G1 cells, accompanied by reduced proportion of S phase cells. Li at concentrations above 2 mM had a significant, dose-dependent, anti-apoptotic effect on the cells undergoing camptothecin induced apoptosis. In conclusion, demonstrated cytoprotective effect of Li is at least partially related to stabilization of mitochondrial membrane potential and to the reduction of DNA damaging effects in proliferating cells; both may form part of the mechanism through which Li is useful in therapy of bipolar disorder, but may have more general consequences.

Association between GSK-3beta -50T/C polymorphism and personality and psychotic symptoms in mood disorders

The exact role of the enzyme glycogen synthase kinase 3beta (GSK-3beta) in mood disorders is still unknown. GSK-3beta has been mapped to chromosome 3q13.3, a potential susceptibility locus for bipolar disorder. The -50T/C polymorphism, falling within the promoter region of the gene coding for GSK-3beta, was previously reported to be associated with age at onset, therapeutic response to lithium salts and total sleep deprivation in bipolar patients. In the present study we investigated the association between the -50T/C polymorphism and both symptomatic and personality features in mood disorders. The sample comprised 365 inpatients affected by major depressive disorder and bipolar disorder, genotyped for the GSK-3beta-50 polymorphism and assessed with the Operational Criteria Checklist for Psychotic Illness (OPCRIT). Ninety-five subjects were also evaluated with the Temperament and Character Inventory (TCI). The GSK-3beta-50 polymorphism showed a positive association with delusional symptomatology and with the personality features linked to Self-Transcendence. Finally, GSK-3beta-50 and personality showed an interactive effect on delusional scores. In conclusion, our findings support the role of GSK-3beta-50 in both normal and psychopathological aspects of human cognition and further suggest a possible interaction between genes and personality in the liability to psychotic disorders.

Activation of glycogen synthase kinase-3 inhibits long-term potentiation with synapse-associated impairments

Activation of glycogen synthase kinase-3 (GSK-3) can cause memory deficits as seen in Alzheimer's disease, the most common age-associated dementia, but the mechanism is not understood. Here, we found that activation of GSK-3 by wortmannin or transient overexpression of wild-type GSK-3beta could suppress the induction of long-term potentiation (LTP) in rat hippocampus, whereas simultaneous inhibition of GSK-3 by lithium or SB216763 or transient expression of a dominant-negative GSK-3beta mutant (dnGSK-3beta) preserved the LTP. After high-frequency stimulation (HFS), the presynaptic release of glutamate and the expression/clustering of synapsin I, a synaptic vesicle protein playing an important role in neurotransmitter release, decreased markedly after upregulation of GSK-3. In vitro studies further demonstrated that GSK-3 inhibited the expression of SynI independent of HFS. In postsynaptic level, the expression of PSD93 and NR2A/B proteins decreased significantly when GSK-3 was activated. The LTP-associated synapse impairments including less presynaptic active zone, thinner postsynaptic density, and broader synaptic cleft were also prominent in the hippocampal slices after HFS with activation of GSK-3. These synaptic impairments were attenuated when GSK-3 was simultaneously inhibited by LiCl or SB216763 or transient expression of dnGSK-3. We conclude that upregulation of GSK-3 impairs the synaptic plasticity both functionally and structurally, which may underlie the GSK-3-involved memory deficits.

Glycogen synthase kinase-3 regulates IGFBP-1 gene transcription through the thymine-rich insulin response element

BACKGROUND

Hepatic expression of several gene products involved in glucose metabolism, including phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase) and insulin-like growth factor binding protein-1 (IGFBP-1), is rapidly and completely inhibited by insulin. This inhibition is mediated through the regulation of a DNA element present in each of these gene promoters, that we call the Thymine-rich Insulin Response Element (TIRE). The insulin signalling pathway that results in the inhibition of these gene promoters requires the activation of phosphatidylinositol 3-kinase (PI 3-kinase). However, the molecules that connect PI 3-kinase to these gene promoters are not yet fully defined. Glycogen Synthase Kinase 3 (GSK-3) is inhibited following activation of PI 3-kinase. We have shown previously that inhibitors of GSK-3 reduce the activity of two TIRE-containing gene promoters (PEPCK and G6Pase), whose products are required for gluconeogenesis.

RESULTS

In this report we demonstrate that in H4IIE-C3 cells, four distinct classes of GSK-3 inhibitor mimic the effect of insulin on a third TIRE-containing gene, IGFBP-1. We identify the TIRE as the minimum requirement for inhibition by these agents, and demonstrate that the target of GSK-3 is unlikely to be the postulated TIRE-binding protein FOXO-1. Importantly, overexpression of GSK-3 in cells reduces the insulin regulation of TIRE activity as well as endogenous IGFBP-1 expression.

CONCLUSIONS

These results implicate GSK-3 as an intermediate in the pathway from the insulin receptor to the TIRE. Indeed, this is the first demonstration of an absolute requirement for GSK-3 inhibition in insulin regulation of gene transcription. These data support the potential use of GSK-3 inhibitors in the treatment of insulin resistant states such as Type 2 diabetes mellitus, but suggest that it will be important to identify all TIRE-containing genes to assess potential side effects of these agents.

Molecular targets of lithium action

Lithium is an effective drug for both the treatment and prophylaxis of bipolar disorder. However, the precise mechanism of lithium action is not yet well understood. Extensive research aiming to elucidate the molecular mechanisms underlying the therapeutic effects of lithium has revealed several possible targets. The behavioral and physiological manifestations of the illness are complex and are mediated by a network of interconnected neurotransmitter pathways. Thus, lithium's ability to modulate the release of serotonin at presynaptic sites and modulate receptor-mediated supersensitivity in the brain remains a relevant line of investigation. However, it is at the molecular level that some of the most exciting advances in the understanding of the long-term therapeutic action of lithium will continue in the coming years. The lithium cation possesses the selective ability, at clinically relevant concentrations, to alter the PI second-messenger system, potentially altering the activity and dynamic regulation of receptors that are coupled to this intracellular response. Subtypes of muscarinic receptors in the limbic system may represent particularly sensitive targets in this regard. Likewise, preclinical data have shown that lithium regulates arachidonic acid and the protein kinase C signaling cascades. It also indirectly regulates a number of factors involved in cell survival pathways, including cAMP response element binding protein, brain-derived neurotrophic factor, bcl-2 and mitogen-activated protein kinases, and may thus bring about delayed long-term beneficial effects via under-appreciated neurotrophic effects. Identification of the molecular targets for lithium in the brain could lead to the elucidation of the pathophysiology of bipolar disorder and the discovery of a new generation of mood stabilizers, which in turn may lead to improvements in the long-term outcome of this devastating illness (1).

Structural insights and biological effects of glycogen synthase kinase 3-specific inhibitor AR-A014418

Glycogen synthase kinase 3 (GSK3) is a serine/threonine kinase that has been implicated in pathological conditions such as diabetes and Alzheimer's disease. We report the characterization of a GSK3 inhibitor, AR-A014418, which inhibits GSK3 (IC50 = 104 +/- 27 nM), in an ATP-competitive manner (Ki = 38 nM). AR-A014418 does not significantly inhibit cdk2 or cdk5 (IC50 > 100 microM) or 26 other kinases demonstrating high specificity for GSK3. We report the co-crystallization of AR-A014418 with the GSK3beta protein and provide a description of the interactions within the ATP pocket, as well as an understanding of the structural basis for the selectivity of AR-A014418. AR-A014418 inhibits tau phosphorylation at a GSK3-specific site (Ser-396) in cells stably expressing human four-repeat tau protein. AR-A014418 protects N2A neuroblastoma cells against cell death mediated by inhibition of the phosphatidylinositol 3-kinase/protein kinase B survival pathway. Furthermore, AR-A014418 inhibits neurodegeneration mediated by beta-amyloid peptide in hippocampal slices. AR-A014418 may thus have important applications as a tool to elucidate the role of GSK3 in cellular signaling and possibly in Alzheimer's disease. AR-A014418 is the first compound of a family of specific inhibitors of GSK3 that does not significantly inhibit closely related kinases such as cdk2 or cdk5.

Mood stabilizer psychopharmacology

Mood stabilizers represent a class of drugs that are efficacious in the treatment of bipolar disorder. The most established medications in this class are lithium, valproic acid, and carbamazepine. In addition to their therapeutic effects for treatment of acute manic episodes, these medications often are useful as prophylaxis against future episodes and as adjunctive antidepressant medications. While important extracellular effects have not been excluded, most available evidence suggests that the therapeutically relevant targets of this class of medications are in the interior of cells. Herein we give a prospective of a rapidly evolving field, discussing common effects of mood stabilizers as well as effects that are unique to individual medications. Mood stabilizers have been shown to modulate the activity of enzymes, ion channels, arachidonic acid turnover, G protein coupled receptors and intracellular pathways involved in synaptic plasticity and neuroprotection. Understanding the therapeutic targets of mood stabilizers will undoubtedly lead to a better understanding of the pathophysiology of bipolar disorder and to the development of improved therapeutics for the treatment of this disease. Furthermore, the involvement of mood stabilizers in pathways operative in neuroprotection suggests that they may have utility in the treatment of classical neurodegenerative disorders.

The Drosophila Wnt, wingless, provides an essential signal for pre- and postsynaptic differentiation

At vertebrate neuromuscular junctions (NMJs), Agrin plays pivotal roles in synapse development, but molecules that activate synapse formation at central synapses are largely unknown. Members of the Wnt family are well established as morphogens, yet recently they have also been implicated in synapse maturation. Here we demonstrate that the Drosophila Wnt, Wingless (Wg), is essential for synapse development. We show that Wg and its receptor are expressed at glutamatergic NMJs, and that Wg is secreted by synaptic boutons. Loss of Wg leads to dramatic reductions in target-dependent synapse formation, and new boutons either fail to develop active zones and postsynaptic specializations or these are strikingly aberrant. We suggest that Wg signals the coordinated development of pre- and postsynaptic compartments.

The Wnt signaling pathway in bipolar disorder

The Wnt signaling pathway is a highly conserved pathway critical for proper embryonic development. However, recent evidence suggests that this pathway and one of its key enzymes, glycogen synthase kinase 3beta, may play important roles in regulating synaptic plasticity, cell survival, and circadian rhythms in the mature CNS-all of which have been implicated in the pathophysiology and treatment of bipolar disorder. Furthermore, two structurally highly dissimilar medications used to treat bipolar disorder, lithium and valproic acid, exert effects on components of the Wnt signaling pathway. Together, these data suggest that the Wnt signaling pathway may play an important role in the treatment of bipolar disorder. Here, the authors review the modulation of the Wnt/GSK-3beta signaling pathway by mood-stabilizing agents, focusing on two therapeutically relevant aspects: neuroprotection and modulation of circadian rhythms. The future development of selective GSK-3beta inhibitors may have considerable utility not only for the treatment of bipolar disorder but also for a variety of classical neurodegenerative disorders.

In utero ethanol suppresses cerebellar activator protein-1 and nuclear factor-kappa B transcriptional activation in a rat fetal alcohol syndrome model

A model of fetal alcohol syndrome was used to investigate prenatal ethanol effects on cerebellar transcription factors. Pregnant Sprague-Dawley rats were divided into three treatment groups: ethanol-exposed (E), calorically matched pair-fed (PF), and freely fed ad libitum (AL) groups. Ethanol exposure was stopped 2 days before parturition. The DNA binding in neonatal cerebella of the redox-sensitive transcription factors nuclear factor-kappa B (NF-kappa B) and activator protein-1 (AP-1) were determined by electrophoretic mobility shift assays. On the first postnatal day (PD1), there was decreased activation of these transcription factors in the E group relative to the control groups. The PD1 transcriptional effects were reversed as the neonate underwent development without further ethanol exposure. Western blot studies showed no corresponding decreases in protein amounts of both AP-1 and NF-kappa B components on PD1. Postnatal glutathione levels and catalase activity, as measures of oxidative stress hypothesized to be a probable cause of the transcriptional effects, showed no statistically significant effects attributable to ethanol. Examination of prenatal cerebella on embryonic day 20 (EM20), a time during ethanol exposure, showed DNA-binding trends similar to those of PD1. EM20 Western blot studies showed decreases in the levels of the active form of glycogen synthase kinase-3 (GSK-3). GSK-3 inhibition was reversed by PD1. Blocking of GSK-3 activity with gestational dietary lithium diminished both AP-1 and NF-kappa B DNA binding. Thus, prenatal ethanol exposure has the effect of diminishing pro-survival transcriptional activation, an effect possibly mediated by changes in GSK-3 activity.

Bipolar disorder

Bipolar, or manic-depressive, disorder is a frequent, severe, mostly recurrent mood disorder associated with great morbidity. The lifetime prevalence of bipolar disorder is 1.3 to 1.6%. The mortality rate of the disease is two to three times higher than that of the general population. About 10-20% of individuals with bipolar disorder take their own life, and nearly one third of patients admit to at least one suicide attempt. The clinical manifestations of the disease are exceptionally diverse. They range from mild hypomania or mild depression to severe forms of mania or depression accompanied by profound psychosis. Bipolar disorder is equally prevalent across sexes, with the exception of rapid cycling, a severe and difficult to treat variant of the disorder, which arises mostly in women. Because of the high risk of recurrence and suicide, long-term prophylactic pharmacological treatment is indicated. Lithium salts are the first choice long-term preventive treatment for bipolar disorder. They also possess well documented antisuicidal effects. Second choice prophylactic treatments are carbamazepine and valproate, although evidence of their effectiveness is weaker.