In vivo regulation of GSK3 phosphorylation by cholinergic and NMDA receptors

Lithium and neuropsychiatric therapeutics: neuroplasticity via glycogen synthase kinase-3beta, beta-catenin, and neurotrophin cascades

Mood disorders are not merely attributed to the functional defect of neurotransmission, but also are due to the structural impairment of neuroplasticity. Chronic stress decreases neurotrophin levels, precipitating or exacerbating depression; conversely, antidepressants increase expression of various neurotrophins (e.g., brain-derived neurotrophic factor and vascular endothelial growth factor), thereby blocking or reversing structural and functional pathologies via promoting neurogenesis. Since the worldwide approval of lithium therapy in 1970, lithium has been used for its anti-manic, antidepressant, and anti-suicidal effects, yet the therapeutic mechanisms at the cellular level remain not-fully defined. During the last five years, multiple lines of evidence have shown that the mood stabilization and neurogenesis by lithium are due to the lithium-induced inhibition of glycogen synthase kinase-3beta (GSK-3beta), allowing accumulation of beta-catenin and beta-catenin-dependent gene transcriptional events. Altered levels of GSK-3beta and beta-catenin are associated with various neuropsychiatric and neurodegenerative diseases, while various classical neuropsychiatric drugs inhibit GSK-3beta and up-regulate beta-catenin expression. In addition, evidence has emerged that insulin-like growth factor-I enhances antidepression, anti-anxiety, memory, neurogenesis, and angiogenesis; antidepressants up-regulate expression of insulin-like growth factor-I, while insulin-like growth factor-I up-regulates brain-derived neurotrophic factor expression and its receptor TrkB level, as well as brain-derived neurotrophic factor-induced synaptic protein levels. More importantly, physical exercise and healthy diet raise transport of peripheral circulating insulin-like growth factor I into the brain, reinforcing the expression of neurotrophins (e.g., brain-derived neurotrophic factor) and the strength of cell survival signalings (e.g., phosphoinositide 3-kinase / Akt / GSK-3beta pathway). This review will focus on the rapidly advancing new trends in the last five years about lithium, GSK-3beta/beta-catenin, and neurotrophin cascades.

Cocaine-induced hyperactivity and sensitization are dependent on GSK3

Glycogen synthase kinase 3 (GSK3) is a critical mediator of many intracellular signaling systems. The activity of GSK3 is regulated by several kinases, with inactivation occurring via phosphorylation of the inhibitory serine-21 (alpha-isoform) and serine-9 (beta-isoform) residues. Here, we investigated whether acute cocaine administration regulates GSK3 activity and if inhibition of GSK3 by valproate or the selective GSK3 inhibitor SB 216763 would attenuate cocaine-induced behaviors in mice. Mice injected with cocaine (20 mg/kg, i.p.) showed a reduction in the phosphorylation of GSK3beta in the caudate putamen, reflecting an increase in the activity of the kinase. To assess the role of GSK3 in cocaine-induced hyperactivity, mice were pretreated with valproate (50-300 mg/kg, i.p.), SB 216763 (0.25-7.5 mg/kg, i.p.), or the appropriate vehicle prior to saline or cocaine (20 mg/kg, i.p.). Valproate or SB 216763 produced significant dose-dependent reductions in cocaine-induced ambulatory and stereotypic activity. Repeated administration of cocaine can result in an augmentation of the locomotor-stimulatory effects of the drug, a phenomenon referred to as sensitization. Mice pretreated with SB 216763 (2.5 mg/kg, i.p.) prior to daily cocaine (20 mg/kg, i.p.) for 5 days showed a significant attenuation of the development of cocaine-induced behavioral sensitization following a cocaine challenge on day 13. These results indicate that cocaine activated GSK3beta in the caudate putamen and that pharmacological inhibition of GSK3 reduced both the acute behavioral responses to cocaine and the long-term neuroadaptations produced by repeated cocaine, therefore suggesting a role for GSK3 in the behavioral and neurochemical manifestations associated with cocaine exposure.

Protective effect of memantine against Doxorubicin toxicity in primary neuronal cell cultures: influence a development stage

One of the serious unwanted effects of the anthracycline anticancer drug doxorubicin (Dox, adriamycin) is its neurotoxicity, which can be evoked by the activation of extracellular (FAS/CD95/Apo-1) pathway of apoptosis in cells. Since memantine, a clinically used N-methyl-D: -aspartic acid (NMDA) receptor antagonist, shows antiapoptotic action in several models of neuronal cell damage, in this study we evaluated the effect of memantine on the cell death induced by Dox in primary neuronal cell cultures. First, we investigated the effect of different concentrations of Dox (0.1-5 microM) on mouse neocortical, hippocampal, striatal, and cerebellar neurons on 7- and 12-day in vitro (DIV). The 7 DIV neuronal cell cultures were more prone to Dox-induced cell death than 12 DIV cultures. The cerebellar neurons were the most resistant to Dox-induced apoptosis in comparison to neuronal cell cultures derived from the forebrain. Memantine (0.1-2 microM) attenuated the Dox-evoked lactate dehydrogenase release in 7 DIV neuronal cell cultures with no significant effect on 12 DIV cultures. The ameliorating effect of memantine on Dox-mediated cell death was also confirmed by an increase in cell viability measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. There was no effect of memantine on Dox-induced caspase-8 and -3 activity and Dox-evoked decrease in mitochondrial potential, although attenuation in the number of cells with apoptotic DNA fragmentation was observed. We also showed that the antiapoptotic effect of memantine in our model was NMDA receptor-independent, since two other antagonists of this receptor, MK-801 and AP-5, did not attenuate Dox-induced cell death. Furthermore, memantine did not influence the Dox-evoked increase in cytoplasmic Ca2+ level. The obtained data suggest developmental regulation of both, the Dox-mediated neurotoxicity and efficacy of memantine in alleviating the Dox-induced cell damage in neuronal cell cultures. Moreover, this neuroprotective effect of memantine seems not to be dependent on caspase-3 activity and on the antagonistic action on NMDA receptor.

Insulin, IGF-1, and muscarinic agonists modulate schizophrenia-associated genes in human neuroblastoma cells

BACKGROUND

Genes associated with energy metabolism are decreased in schizophrenia brain and human and rodent diabetic skeletal muscle. These and other similarities between diabetes and schizophrenia suggest that an insulin signaling deficit may underlie schizophrenia. We determined with human SH-SY5Y neuroblastoma and astrocyte cell lines whether insulin or other molecules could modulate genes opposite to their change reported in schizophrenia brain.

METHODS

Both cell lines were treated with insulin, insulin-like growth factor (IGF)-1, IGF-2, or brain-derived neurotrophic factor (BDNF). Genes whose expression was found with microarrays to be changed by insulin in a reciprocal manner to their change in schizophrenia were used in a 16-gene miniarray to identify small molecules that might mimic insulin.

RESULTS

Insulin phosphorylated its receptor in the neuroblastoma cells but not in astrocytes and, like IGF-1, increased ERK1/2 and Akt phosphorylation. Insulin and IGF-1 increased the expression of genes decreased in schizophrenia, including those involved in mitochondrial functions, glucose and energy metabolism, hydrogen ion transport, and synaptic function. These gene effects were confirmed and shown to be dose related with the 16-gene miniarrays. Most of 1940 pharmacologically unique compounds failed to alter gene expression, with the exception of muscarinic agonists, which mimicked insulin and IGF-1, and which were blocked by the muscarinic antagonists atropine and telenzepine.

CONCLUSIONS

Stimulation of muscarinic and insulin/IGF-1 receptors alter genes associated with metabolic and synaptic functions in a manner reciprocal to their changes in schizophrenia. Pharmacologic activation of these receptors may normalize genomic alterations in schizophrenia and better address root causes of this disease.

Elevated glycogen synthase kinase-3 activity in Fragile X mice: key metabolic regulator with evidence for treatment potential

Significant advances have been made in understanding the underlying defects of and developing potential treatments for Fragile X syndrome (FXS), the most common heritable mental retardation. It has been shown that neuronal metabotropic glutamate receptor 5 (mGluR5)-mediated signaling is affected in FX animal models, with consequent alterations in activity-dependent protein translation and synaptic spine functionality. We demonstrate here that a central metabolic regulatory enzyme, glycogen synthase kinase-3 (GSK3) is present in a form indicating elevated activity in several regions of the FX mouse brain. Furthermore, we show that selective GSK3 inhibitors, as well as lithium, are able to revert mutant phenotypes of the FX mouse. Lithium, in particular, remained effective with chronic administration, although its effects were reversible even when given from birth. The combination of an mGluR5 antagonist and GSK3 inhibitors was not additive. Instead, it was discovered that mGluR5 signaling and GSK3 activation in the FX mouse are coordinately elevated, with inhibition of mGluR5 leading to inhibition of GSK3. These findings raise the possibility that GSK3 is a fundamental and central component of FXS pathology, with a substantial treatment potential.

Cholinergic treatments with emphasis on m1 muscarinic agonists as potential disease-modifying agents for Alzheimer's disease

The only prescribed drugs for treatment of Alzheimer's disease (AD) are acetylcholinesterase inhibitors (e.g., donepezil, rivastigmine, galantamine, and tacrine) and memantine, an NMDA antagonist. These drugs ameliorate mainly the symptoms of AD, such as cognitive impairments, rather than halting or preventing the causal neuropathology. There is currently no cure for AD and there is no way to stop its progression, yet there are numerous therapeutic approaches directed against various pathological hallmarks of AD that are extensively being pursued. In this context, the three major hallmark characteristics of AD (i.e., the CNS cholinergic hypofunction, formation of beta-amyloid plaques, and tangles containing hyperphosphorylated tau proteins) are apparently linked. Such linkages may have therapeutic implications, and this review is an attempt to analyze these versus the advantages and drawbacks of some cholinergic compounds, such as acetylcholinesterase inhibitors, M1 muscarinic agonists, M2 antagonists, and nicotinic agonists. Among the reviewed treatments, M1 selective agonists emerge, in particular, as potential disease modifiers.

Interaction between Neuronal Depolarization and MK-801 in SH-SY5Y Cells and the Rat Cortex

OBJECTIVE

The interaction between MK-801, a model of psychosis and KCl-induced depolarization or electroconvulsive shock (ECS), a therapeutic model of electroconvulsive therapy (ECT), was investigated in SH-SY5Y cells and the rat frontal cortex.

METHODS

SH-SY5Y cells were pretreated with 1 microM MK-801 for 15 min, followed by cotreatment with 100 mM KCl for 5 min. MK-801 was reintroduced after the KCl was washed out, and the samples were incubated before harvesting. For the experiments in rats, male Sprague-Dawley rats were treated with MK-801 followed by ECS. Immunoblot analyses of glycogen synthase kinase 3beta (GSK3beta) (Ser9), AKT (Ser473) and extracellular legulated kinase (ERK)1/2 in SH-SY5Y cells and the rat frontal cortex were performed.

RESULTS

KCl-induced neuronal depolarization resulted in the transient dephosphorylation of AKT (Ser473) and GSK3beta (Ser9), followed by increased phosphorylation of the enzymes in SH-SY5Y cells. Cotreatment with MK-801 and KCl inhibited the initial dephosphorylation of AKT and GSK3beta produced by KCl-induced neuronal depolarization. Similarly, ECS resulted in the transient dephosphorylation of AKT (Ser473) and GSK3beta (Ser9), whereas cotreatment with MK-801 inhibited the initial dephosphorylation of AKT (Ser473) and GSK3beta (Ser9) produced by ECS in the rat frontal cortex. No significant interaction was observed between MK-801 and KCl in the dephosphorylation of ERK1/2.

CONCLUSION

These results suggest that an antagonistic interplay between MK-801 and neuronal depolarization by KCl or ECS is involved the regulation of AKT (Ser473) and GSK3beta (Ser9) phosphorylation.

Microtubule-associated protein tau in development, degeneration and protection of neurons

As a principal neuronal microtubule-associated protein, tau has been recognized to play major roles in promoting microtubule assembly and stabilizing the microtubules and to maintain the normal morphology of the neurons. Recent studies suggest that tau, upon alternative mRNA splicing and multiple posttranslational modifications, may participate in the regulations of intracellular signal transduction, development and viability of the neurons. Furthermore, tau gene mutations, aberrant mRNA splicing and abnormal posttranslational modifications, such as hyperphosphorylation, have also been found in a number of neurodegenerative disorders, collectively known as tauopathies. Therefore, changes in expression of the tau gene, alternative splicing of its mRNA and its posttranslational modification can modulate the normal architecture and functions of neurons as well as in a situation of tauopathies, such as Alzheimer's disease. The primary aim of this review is to summarize the latest developments and perspectives in our understanding about the roles of tau, especially hyperphosphorylation, in the development, degeneration and protection of neurons.

Glutamatergic approaches to the treatment of cognitive and behavioural symptoms of Alzheimer's disease

The glutamatergic system has long been recognised for its role in learning and memory and recent studies indicate an early loss of glutamatergic synapses in Alzheimer's disease (AD). Efforts to produce drugs which address changes in the glutamatergic system in AD are well advanced (e.g. memantine and drugs in development such as ampakines). Much less is known about the possible role of glutamate in non-cognitive behavioural changes; however, recent data from clinical trials suggest that memantine reduces agitation and aggressive behaviour in AD patients. In this context, it is important to help identify new treatment approaches to replace the use of antipsychotics in this vulnerable population.

Honeybee Apis mellifera acetylcholinesterase--a biomarker to detect deltamethrin exposure

The purpose of this study is to investigate the possibility to use acetylcholinesterase (AChE) as a biomarker of exposure to deltamethrin insecticide in the honeybee, Apis mellifera and to test its reliability in the presence of other contaminants, as carbamate insecticide. Joined actions of deltamethrin (pyrethroid) and pirimicarb (carbamate), alone or in association, are investigated on AChE activity in surviving and dead honeybees, with a special focus on the relative proportions of its membrane and soluble forms. At the 0.5X dose (12.5 ng of deltamethrin and/or 2.5 microg of pirimicarb per bee), the residual tissue AChE activity in dead bees was 78% with deltamethrin, 43% with pirimicarb and 33% with dual treatment. In surviving bees, tissue AChE activity represented 250%, and 270% of control AChE activity with deltamethrin and dual treatment, respectively. The analysis of membrane and soluble AChE forms revealed an increase in the soluble form in dead bees after deltamethrin and dual treatment. However, in vitro investigations showed no direct interaction of deltamethrin on soluble and membrane AChE activity. The results suggest that the action of deltamethrin on AChE activity, in honeybee intact organisms, could be due to indirect mechanisms. The duality of AChE response to deltamethrin exposure, exhibited by the possibility of increase (surviving bees) or decrease (dead bees) of its activity has been pointed out for the first time. The important increase in AChE activity in response to deltamethrin, not altered by pirimicarb treatment, suggests that AChE activity could represent a robust biomarker specific to deltamethrin exposure in living bees.

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.

The attenuating effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in human neuroblastoma SH-SY5Y cells

Memantine, a clinically used N-methyl-D-aspartate (NMDA)-receptor antagonist, has been shown to prevent apoptotic neuronal damage connected with the over-activity of NMDA receptors. In the present study, we examined the effect of memantine on staurosporine-, salsolinol- and doxorubicin-induced apoptosis in the SH-SY5Y cell line which does not possess functional NMDA receptors. Electrophysiological recordings and toxicity studies showed no response to NMDA-evoked currents in this cell line, irrespective of the stage of its neuronal differentiation. Memantine (0.1-2 microM) attenuated staurosporine-induced apoptosis as evidenced by reversal of the changes in mitochondrial membrane potential (DeltaPsi(m)) and decreased caspase-3 activity, lactate dehydrogenase (LDH) release and DNA fragmentation. Wortmannin (10 nM) and LY 294002 (10 microM) (inhibitors of phosphatidylinositol-3-kinase, PI3-K) reversed the inhibitory effect of memantine on the staurosporine-induced LDH release, suggesting that the PI3-K/Akt prosurvival pathway is a possible target for antiapoptotic action of memantine. Memantine at low micromolar concentrations also attenuated salsolinol- and doxorubicin-induced LDH release and DNA fragmentation, but only in the case of salsolinol was this effect accompanied by a decrease in caspase-3 activity. The present data indicate that memantine attenuates the toxic effects of various proapoptotic agents and the cytoprotective effect of memantine does not seem to be connected with its action on NMDA receptor but rather with its influence on intracellular pathways engaged in cellular survival/apoptotic processes.

Dehydroevodiamine attenuates tau hyperphosphorylation and spatial memory deficit induced by activation of glycogen synthase kinase-3 in rats

Tau hyperphosphorylation and memory deficit are characteristic alterations of Alzheimer's disease (AD), and glycogen synthase kinase-3 (GSK-3) plays a crucial role in these AD-like changes. We have reported that activation of GSK-3 through ventricular injection of wortmannin and GF-109203X (WT/GFX, 100 microM each) induces tau hyperphosphorylation and memory impairment of rats [Liu, S.J. et al., 2003. Overactivation of glycogen synthase kinase-3 by inhibition of phosphoinositol-3 kinase and protein kinase C leads to hyperphosphorylation of tau and impairment of spatial memory. J. Neurochem. 87, 1333-1344]. By using this model, we explored in the present study the effects of dehydroevodiamine (DHED), a quinazoline alkaloid isolated from Evodia rutaecarpa Bentham, on the memory retention, tau phosphorylation and the activity of GSK-3. We found that pre-administration of DHED through vena caudalis for 1 week efficiently improved the WT/GFX-induced spatial memory retention impairment of the rats; it also antagonized tau hyperphosphorylation at multiple AD sites and arrested the overactivation of GSK-3 induced by WT/GFX. Our study gave the first in vivo evidence that DHED could suppress the overactivation of GSK-3 and improve tau hyperphosphorylation and spatial memory deficit of the rats, suggesting that this chemical may be served as a candidate for arresting AD-like pathological and behavioral alterations.

Potential role of N-methyl-D-aspartate receptors as executors of neurodegeneration resulting from diverse insults: focus on memantine

Glutamatergic neurotransmission is critical to normal learning and memory and when the activity of glutamate neurons becomes excessive, or the normal function of its primary receptors becomes dysfunctional, this may lead to pathological changes associated with age-related neurodegenerative diseases. Anomalous glutamatergic activity associated with Alzheimer's disease may be due to a postsynaptic receptor and downstream defects that produce inappropriately timed or sustained glutamate activation of N-methyl-D-aspartate receptors, leading to neuronal injury and death and cognitive deficits associated with dementia. The mechanisms leading to the condition of chronically depolarized membranes on vulnerable neurons in the Alzheimer's disease brain are likely due to a complex interaction between oxidative stress, mitochondrial failure, chronic brain inflammation and the presence of amyloid-beta and hyperphosphorylated-tau; each of these factors are highly interrelated with each other and are discussed with an emphasis upon potential therapeutic mechanisms underlying the neuroprotective actions of memantine.

Glycogen synthase kinase-3 (GSK3) in psychiatric diseases and therapeutic interventions

Glycogen synthase kinase-3 (GSK3) has recently been linked to mood disorders and schizophrenia, and the neurotransmitter systems and therapeutic treatments associated with these diseases. GSK3 is a widely influential enzyme that is capable of phosphorylating, and thereby regulating, over forty known substrates. Four mechanisms regulating GSK3 (phosphorylation, protein complexes, localization, and substrate phosphorylation) combine to provide substrate-specific regulation of the actions of GSK3. Several intracellular signaling cascades converge on GSK3 to modulate its activity, and several neurotransmitter systems also regulate GSK3, including serotonergic, dopaminergic, cholinergic, and glutamatergic systems. Because of changes in these neurotransmitter systems and the actions of therapeutic drugs, GSK3 has been linked to the mood disorders, bipolar disorder and depression, and to schizophrenia. Inhibition of GSK3 may be an important therapeutic target of mood stabilizers, and regulation of GSK3 may be involved in the therapeutic effects of other drugs used in psychiatry. Dysregulated GSK3 in bipolar disorder, depression, and schizophrenia could have multiple effects that could impair neural plasticity, such as modulation of neuronal architecture, neurogenesis, gene expression, and the ability of neurons to respond to stressful, potentially lethal, conditions. In part because of these key actions of GSK3 and its associations with mood disorders and schizophrenia, much research is currently being devoted to identifying new selective inhibitors of GSK3.

Effects of Glycogen Synthase Kinase 3β and Cyclin-Dependent Kinase 5 Inhibitors on Morphine-Induced Analgesia and Tolerance in Rats

Repeated administration of morphine is associated with the development of tolerance, yet the mechanism underlying this phenomenon is still poorly understood. Recent evidence implicating glycogen synthase kinase 3 (GSK3) in opioid receptor signaling pathways has prompted us to investigate its role in morphine tolerance. Administration of 10 mg/kg morphine i.p. to Wistar rats twice daily for 8 days resulted in complete tolerance to its analgesic effects as measured by the tail-flick test. When injections of morphine were preceded by intrathecal (i.t.) administration of either an inhibitor of GSK3 [(3-(2,4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione (SB216763) or 6-bromoindirubin-3'oxime] or an inhibitor of cyclin-dependent kinase (Cdk), roscovitine, development of tolerance to morphine analgesia was completely abolished. In addition, a single i.t. injection of either kinase inhibitor was able to restore in a dose-dependent manner the analgesic effect of morphine in morphine-tolerant rats. None of the inhibitors in doses used in the present study had analgesic effects of their own nor an effect on the analgesic potency of morphine. Repeated i.t. administration of either inhibitor had caused an increase in abundance of GSK-3beta phosphorylated at Ser(9) in the dorsal lumbar part of the spinal cord of rats that were chronically treated with morphine. Furthermore, reversal of morphine tolerance by a single injection of either inhibitor was always associated with increased abundance of phospho-GSK3beta. In conclusion, our data indicate that chronic morphine treatment activates a highly efficient pathway by means of which Cdk5 regulates GSK3beta activity.