Differential effects of the antipsychotics haloperidol and clozapine on G protein measures in mononuclear leukocytes of patients with schizophrenia

A Role for Phosphodiesterase 11A (PDE11A) in the Formation of Social Memories and the Stabilization of Mood

The most recently discovered 3',5'-cyclic nucleotide phosphodiesterase family is the Phosphodiesterase 11 (PDE11) family, which is encoded by a single gene PDE11A. PDE11A is a dual-specific PDE, breaking down both cAMP and cGMP. There are four PDE11A splice variants (PDE11A1-4) with distinct tissue expression profiles and unique N-terminal regulatory regions, suggesting that each isoform could be individually targeted with a small molecule or biologic. PDE11A4 is the PDE11A isoform expressed in brain and is found in the hippocampal formation of humans and rodents. Studies in rodents show that PDE11A4 mRNA expression in brain is, in fact, restricted to the hippocampal formation (CA1, possibly CA2, subiculum, and the adjacently connected amygdalohippocampal area). Within the hippocampal formation of rodents, PDE11A4 protein is expressed in neurons but not astrocytes, with a distribution across nuclear, cytoplasmic, and membrane compartments. This subcellular localization of PDE11A4 is altered in response to social experience in mouse, and in vitro studies show the compartmentalization of PDE11A4 is controlled, at least in part, by homodimerization and N-terminal phosphorylation. PDE11A4 expression dramatically increases in the hippocampus with age in the rodent hippocampus, from early postnatal life to late aging, suggesting PDE11A4 function may evolve across the lifespan. Interestingly, PDE11A4 protein shows a three to tenfold enrichment in the rodent ventral hippocampal formation (VHIPP; a.k.a. anterior in primates) versus dorsal hippocampal formation (DHIPP). Consistent with this enrichment in VHIPP, studies in knockout mice show that PDE11A regulates the formation of social memories and the stabilization of mood and is a critical mechanism by which social experience feeds back to modify the brain and subsequent social behaviors. PDE11A4 likely controls behavior by regulating hippocampal glutamatergic, oxytocin, and cytokine signaling, as well as protein translation. Given its unique tissue distribution and relatively selective effects on behavior, PDE11A may represent a novel therapeutic target for neuropsychiatric, neurodevelopmental, or age-related disorders. Therapeutically targeting PDE11A4 may be a way to selectively restore aberrant cyclic nucleotide signaling in the hippocampal formation while leaving the rest of the brain and periphery untouched, thus, relieving deficits while avoiding unwanted side effects.

PDE11A regulates social behaviors and is a key mechanism by which social experience sculpts the brain

Despite the fact that appropriate social behaviors are vital to thriving in one's environment, little is understood of the molecular mechanisms controlling social behaviors or how social experience sculpts these signaling pathways. Here, we determine if Phosphodiesterase 11A (PDE11A), an enzyme that is enriched in the ventral hippocampal formation (VHIPP) and that breaks down cAMP and cGMP, regulates social behaviors. PDE11 wild-type (WT), heterozygous (HT), and knockout (KO) mice were tested in various social approach assays and gene expression differences were measured by RNA sequencing. The effect of social isolation on PDE11A4 compartmentalization and subsequent social interactions and social memory was also assessed. Deletion of PDE11A triggered age- and sex-dependent deficits in social approach in specific social contexts but not others. Mice appear to detect altered social behaviors of PDE11A KO mice, because C57BL/6J mice prefer to spend time with a sex-matched PDE11A WT vs. its KO littermate; whereas, a PDE11A KO prefers to spend time with a novel PDE11A KO vs. its WT littermate. Not only is PDE11A required for intact social interactions, we found that 1month of social isolation vs. group housing decreased PDE11A4 protein expression specifically within the membrane fraction of VHIPP. This isolation-induced decrease in PDE11A4 expression appears functional because social isolation impairs subsequent social approach behavior and social memory in a PDE11A genotype-dependent manner. Pathway analyses following RNA sequencing suggests PDE11A is a key regulator of the oxytocin pathway and membrane signaling, consistent with its pivotal role in regulating social behavior.

Brain CB₂ Receptors: Implications for Neuropsychiatric Disorders

Although previously thought of as the peripheral cannabinoid receptor, it is now accepted that the CB₂ receptor is expressed in the central nervous system on microglia, astrocytes and subpopulations of neurons. Expression of the CB₂ receptor in the brain is significantly lower than that of the CB₁ receptor. Conflicting findings have been reported on the neurological effects of pharmacological agents targeting the CB₂ receptor under normal conditions. Under inflammatory conditions, CB₂ receptor expression in the brain is enhanced and CB₂ receptor agonists exhibit potent anti-inflammatory effects. These findings have prompted research into the CB₂ receptor as a possible target for the treatment of neuroinflammatory and neurodegenerative disorders. Neuroinflammatory alterations are also associated with neuropsychiatric disorders and polymorphisms in the CB₂ gene have been reported in depression, eating disorders and schizophrenia. This review will examine the evidence to date for a role of brain CB₂ receptors in neuropsychiatric disorders.

Developmental etiology for neuroanatomical and cognitive deficits in mice overexpressing Galphas, a G-protein subunit genetically linked to schizophrenia

Schizophrenia is a widespread psychiatric disorder, affecting 1% of people. Despite this high prevalence, schizophrenia is not well treated because of its enigmatic developmental origin. We explore here the developmental etiology of endophenotypes associated with schizophrenia using a regulated transgenic approach in mice. Recently, a polymorphism that increases mRNA levels of the G-protein subunit Galphas was genetically linked to schizophrenia. Here we show that regulated overexpression of Galphas mRNA in forebrain neurons of mice is sufficient to cause a number of schizophrenia-related phenotypes, as measured in adult mice, including sensorimotor gating deficits (prepulse inhibition of acoustic startle, PPI) that are reversed by haloperidol or the phosphodiesterase inhibitor rolipram, psychomotor agitation (hyperlocomotion), hippocampus-dependent learning and memory retrieval impairments (hidden water maze, contextual fear conditioning), and enlarged ventricles. Interestingly, overexpression of Galphas during development plays a significant role in some (PPI, spatial learning and memory and neuroanatomical deficits) but not all of these adulthood phenotypes. Pharmacological and biochemical studies suggest the Galphas-induced behavioral deficits correlate with compensatory decreases in hippocampal and cortical cyclic AMP (cAMP) levels. These decreases in cAMP may lead to reduced activation of the guanine exchange factor Epac (also known as RapGEF 3/4) as stimulation of Epac with the select agonist 8-pCPT-2'-O-Me-cAMP increases PPI and improves memory in C57BL/6J mice. Thus, we suggest that the developmental impact of a given biochemical insult, such as increased Galphas expression, is phenotype specific and that Epac may prove to be a novel therapeutic target for the treatment of both developmentally regulated and non-developmentally regulated symptoms associated with schizophrenia.

Multifunctional pharmacotherapy: what can we learn from study of selective serotonin reuptake inhibitor augmentation of antipsychotics in negative-symptom schizophrenia?

Many patients suffering from major psychiatric disorders do not respond adequately to monotherapy and require additional drugs. To date, there are no objective guidelines for deciding which combination may be effective, and the choice is based on previous clinical experience and on trial and error. Even when combination drugs are effective, the biochemical mechanisms responsible for the value-added effect are unknown. Understanding the mechanism of such synergism may provide a rational basis for choosing drug combinations and for developing more effective drugs. In schizophrenia, negative symptoms respond poorly to antipsychotics, but may improve when these are augmented with selective serotonin reuptake inhibitors (SSRI). This augmenting effect cannot be explained by summating the pharmacological effects of the individual drugs. We proposed that the study of SSRI augmentation can serve as a window to understanding the biochemical mechanisms of clinically effective drug synergism. In a series of studies we identified unique biochemical effects of the combination, different from each individual drug, and proposed that some of these are involved in mediating the clinical effect. Here we review some of the findings and propose that the mechanism of action involves regionally selective modulation of the GABA system. The evidence indicates that the SSRI antidepressant-antipsychotic combination may be a useful paradigm for studying therapeutically effective synergistic drug interactions in schizophrenia. Although as yet limited in scope, the findings of definable molecular targets for synergistic SSRI-antipsychotic interaction provide new directions to inform future research and provide novel bio-molecular targets for drug development.

Nonverbal delayed recognition in the relatives of schizophrenia patients with or without schizophrenia spectrum

BACKGROUND

There is increased interest in the study of cognitive deficits as possible endophenotypic markers for schizophrenia. The main goal of this study was to determine how familiality and schizophrenia spectrum personality symptomatology are related to performance of auditory and visuospatial delayed recognition memory tasks.

METHODS

The study sample consisted of 162 subjects divided into five groups. The groups included 39 patients with a DSM-IV diagnosis of schizophrenia or schizophreniform disorder; first-degree relatives of schizophrenia patients, 22 with and 31 without schizophrenia spectrum personality traits; and healthy control subjects with no family history of psychosis, 22 with and 48 without schizophrenia spectrum traits. Auditory and visuospatial delayed recognition memory performance was assessed.

RESULTS

Significant differences were observed between patients and healthy control subjects in both auditory [F(1,79) = 7.358 p = .008] and visual [F(1,47) = 34.67, p < .001] delayed recognition tasks. When comparing the four non-patient groups, auditory and visuospatial discriminability decreased as a function of familiality of schizophrenia (p < .05). Deficits were more pronounced in relatives with schizophrenia spectrum traits [auditory d = .7114; visual d = 1.0199].

CONCLUSIONS

A biological relationship to schizophrenia increases the likelihood of impaired delayed recognition memory. Likewise, poorer performance is associated with schizophrenia spectrum phenotype only when combined with familiality.

Possible association between G-protein β3 subunit C825T polymorphism and antipsychotic-induced restless legs syndrome in schizophrenia

OBJECTIVE

The incidence of restless legs syndrome (RLS) is presumed to be higher among people with schizophrenia who take antipsychotic medication, most of which blocks the dopamine D2 receptor. The purpose of this study was to determine whether the G-protein β3 subunit (GNB3) C825T polymorphism is associated with antipsychotic-induced RLS in schizophrenia.

METHODS

We examined 178 Korean patients with schizophrenia. All of the subjects were evaluated using the diagnostic criteria of the International Restless Legs Syndrome Study Group and the International Restless Legs Scale. Genotyping was performed for the C825T polymorphism in the GNB3 gene.

RESULTS

The genotype distribution did not differ significantly between antipsychotic-induced RLS patients and patients who had no-RLS symptoms (χ 2 = 4.30, p = 0.116). The genotypes of the C825T single-nucleotide polymorphism (SNP) were classified into two groups: C+ (CC and CT genotypes) and C- (TT genotype). The presence of the C allele (C+) was associated with an increased likelihood of RLS (χ 2 = 4.14, p = 0.042; odds ratio = 2.56, 95% confidence interval = 1.02-6.47).

CONCLUSIONS

These results suggest that the GNB3 C825T SNP is associated with RLS in schizophrenia. However, confirming this association requires future larger scale studies in which the effects of medication are strictly controlled.

Gene expression changes in peripheral mononuclear cells from schizophrenic patients treated with a combination of antipsychotic with fluvoxamine

Antipsychotic treatment combined with Selective Serotonin Reuptake Inhibitor (SSRI) antidepressant can improve negative symptoms in schizophrenic patients that are unresponsive to antipsychotic drugs alone. The mechanism of this therapeutic effect is not clear. The current study examined molecular changes induced by the combined treatment in human peripheral mononuclear cells (PMC) in order to get insight into its mechanism of action. Gene expression profile of PMC from antipsychotic-treated patients was examined before addition of the SSRI fluvoxamine, and 3 and 6 weeks after. Gene expression patterns screened with a cDNA array, comprising 1176 genes, revealed homologous changes in a range of transcripts related to G-protein coupled receptors (GPCR). Genes related to GPCR-family were assayed using customized cDNA array and the results verified by real-time RT-PCR. The mRNA expression of chemokine receptors, IL8RA and CCR1, and of RGS7 was significantly down-regulated following fluvoxamine augmentation. The clinical assessments showed improvement in negative symptoms following the combined treatment. The transcriptional analysis suggests that the therapeutic mechanism of the combined antipsychotic-fluvoxamine treatment may involve genes associated with G-protein coupled receptors (GPCR). Our findings suggest that gene expression changes in PMC may be useful in investigating the mechanism of drug action in schizophrenia.

Serotonin 1a receptor and associated G-protein activation in schizophrenia and bipolar disorder

Abnormalities in the serotonergic signalling system, including the serotonin 1a receptor, have been implicated in the pathogenesis of schizophrenia and bipolar 1 disorder. However, there is no consensus on whether the density of the serotonin 1a receptor and/or the activity of the G-proteins linking the receptor to the intracellular cascade are altered in these disease states. To address these issues, tissue obtained postmortem from four cortical regions was used to measure [3H] 8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) binding and 8-OH-DPAT-stimulated guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) binding to determine if either parameter is altered in schizophrenia or bipolar I disorder. There was an effect of diagnosis on the level of [3H] 8-OH-DPAT binding that may indicate a global change in the density of serotonin 1a receptors, although this effect did not reach significance in any individual brain region. The activation of serotonin 1a receptors did not differ significantly with diagnoses. However, in the outer cortical layers, there appeared to be a dissociation between the number of receptors available and the extent of ligand-induced GTPgammaS binding, suggesting considerable receptor reserve. In addition, comparing gender independent of diagnoses, a decrease in the levels of serotonin 1a receptors was observed in the cortex of female subjects. These data indicates that there may be subtle changes in serotonin 1a receptors across the cortex in schizophrenia or bipolar I disorder and suggests a gender discordance in receptor levels.

Gi/Go protein-dependent presynaptic mechanisms are involved in clozapine-induced down-regulation of tyrosine hydroxylase in PC12 cells

Although the clinical effects of antipsychotics have been extensively studied, the molecular mechanisms underlying their antipsychotic activity are unclear. Chronic clozapine has been reported to reduce significantly the expression of tyrosine hydroxylase (TH) in the mesolimbic system. To characterize the mechanisms of action of clozapine on TH expression, PC12 cells turned out to be a useful model, being by far less complex than the entire brain. Both the quantity of TH protein and the amount of TH mRNA in PC12 cells were found to be decreased during incubation of the cells in the presence of clozapine. This decline was followed by a decrease in the enzymatic activity of TH. The effect of clozapine was blocked by preincubation with N-ethylmaleimide, a sulphydryl-alkylating reagent that interferes in Gi/o protein-mediated second messenger pathways. Clozapine may thus decrease TH expression by interacting with Gi/o protein-coupled receptors, such as D2 and 5HT1A. Knowledge of the molecular mechanisms underlying the clinical effects of established antipsychotics will promote the development of new and more efficient antipsychotic drugs.

Sensorimotor gating deficits in transgenic mice expressing a constitutively active form of Gs alpha

Schizophrenia is a complex disorder characterized by wide-ranging cognitive impairments, including deficits in learning as well as sensory gating. The causes of schizophrenia are unknown, but alterations in intracellular G-protein signaling pathways are among the molecular changes documented in patients with schizophrenia. Using the CaMKIIalpha promoter to drive expression in neurons within the forebrain, we have developed transgenic mice that express a constitutively active form of G(s)alpha (G(s)alpha(*)), the G protein that couples receptors such as the D(1) and D(5) dopamine receptors to adenylyl cyclase. We have also generated mice in which the CaMKIIalpha promoter drives expression of a dominant-negative form of protein kinase A, R(AB). Here, we examine startle responses and prepulse inhibition of the startle reflex (PPI) in these G(s)alpha(*) and R(AB) transgenic mice. G(s)alpha(*) transgenic mice exhibited selective deficits in PPI, without exhibiting alterations in the startle response, whereas no deficit in startle or PPI was found in the R(AB) transgenic mice. Thus, overstimulation of the cAMP/PKA pathway disrupts PPI, but the cAMP/PKA pathway may not be essential for sensorimotor gating. G(s)alpha(*) transgenic mice may provide an animal model of certain endophenotypes of schizophrenia, because of the similarities between them and patients with schizophrenia in G-protein function, hippocampus-dependent learning, and sensorimotor gating.

Endocannabinoid signalling in the blood of patients with schizophrenia

AIM

To test the hypothesis that schizophrenia might be associated with alterations of the endogenous cannabinoid system in human blood.

RESULTS

Blood from 20 healthy volunteers and 12 patients with schizophrenia, 5 of which both before and after a successful antipsychotic treatment, was analysed for: 1) the amounts of the endocannabinoid anandamide; 2) the levels of cannabinoid CB1 and CB2 receptor mRNAs, and 3) the levels of the mRNA encoding the enzyme fatty acid amide hydrolase (FAAH), responsible for anandamide degradation. The amounts of anandamide were significantly higher in the blood of patients with acute schizophrenia than in healthy volunteers (7.79 +/- 0.50 vs. 2.58 +/- 0.28 pmol/ml). Clinical remission was accompanied by a significant decrease of the levels of anandamide (3.88 +/- 0.72 pmol/ml) and of the mRNA transcripts for CB2 receptors and FAAH.

CONCLUSION

These findings indicate that endocannabinoid signalling might be altered during the acute phase of schizophrenia not only in the central nervous system but also in the blood. These changes might be related to the several immunological alterations described in schizophrenia.

Application of G-proteins in the molecular diagnosis of psychiatric disorders

Mental disorders are highly prevalent and often difficult to diagnose. Although significant advances have been achieved in medication for mental disorders, the diagnosis and treatment monitoring of these disorders remain in a static situation. The absence of objective diagnostic 'gold standards', derives from the special complexity of diagnosis in psychiatry. Heterotrimeric G-proteins are crucial elements in post-receptor information transduction. These proteins have been implicated in the biochemical mechanism of action of drugs used to treat psychiatric disorders. G-protein measurements have unravelled a differential pattern characteristic of each of the major mental disorders. The accumulated data supports the potential use of G-protein measures as state-dependent markers for the biochemical diagnosis of mental disorders and as aid in the biochemical monitoring of the response to a specific treatment.