Regulation of regulators of G protein signaling mRNA expression in rat brain by acute and chronic electroconvulsive seizures

RGS4 Actions in Mouse Prefrontal Cortex Modulate Behavioral and Transcriptomic Responses to Chronic Stress and Ketamine

The signal transduction protein, regulator of G protein signaling 4 (RGS4), plays a prominent role in physiologic and pharmacological responses by controlling multiple intracellular pathways. Our earlier work identified the dynamic but distinct roles of RGS4 in the efficacy of monoamine-targeting versus fast-acting antidepressants. Using a modified chronic variable stress (CVS) paradigm in mice, we demonstrate that stress-induced behavioral abnormalities are associated with the downregulation of RGS4 in the medial prefrontal cortex (mPFC). Knockout of RGS4 (RGS4KO) increases susceptibility to CVS, as mutant mice develop behavioral abnormalities as early as 2 weeks after CVS resting-state functional magnetic resonance imaging I (rs-fMRI) experiments indicate that stress susceptibility in RGS4KO mice is associated with changes in connectivity between the mediodorsal thalamus (MD-THL) and the mPFC. Notably, RGS4KO also paradoxically enhances the antidepressant efficacy of ketamine in the CVS paradigm. RNA-sequencing analysis of naive and CVS samples obtained from mPFC reveals that RGS4KO triggers unique gene expression signatures and affects several intracellular pathways associated with human major depressive disorder. Our analysis suggests that ketamine treatment in the RGS4KO group triggers changes in pathways implicated in synaptic activity and responses to stress, including pathways associated with axonal guidance and myelination. Overall, we show that reducing RGS4 activity triggers unique gene expression adaptations that contribute to chronic stress disorders and that RGS4 is a negative modulator of ketamine actions. SIGNIFICANCE STATEMENT: Chronic stress promotes robust maladaptation in the brain, but the exact intracellular pathways contributing to stress vulnerability and mood disorders have not been thoroughly investigated. In this study, the authors used murine models of chronic stress and multiple methodologies to demonstrate the critical role of the signal transduction modulator regulator of G protein signaling 4 in the medial prefrontal cortex in vulnerability to chronic stress and the efficacy of the fast-acting antidepressant ketamine.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

The Emerging Key Role of the mGluR1-PKCγ Signaling Pathway in the Pathogenesis of Spinocerebellar Ataxias: A Neurodevelopmental Viewpoint

Spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominantly inherited progressive disorders with degeneration and dysfunction of the cerebellum. Although different subtypes of SCAs are classified according to the disease-associated causative genes, the clinical syndrome of the ataxia is shared, pointing towards a possible convergent pathogenic pathway among SCAs. In this review, we summarize the role of SCA-associated gene function during cerebellar Purkinje cell development and discuss the relationship between SCA pathogenesis and neurodevelopment. We will summarize recent studies on molecules involved in SCA pathogenesis and will focus on the mGluR1-PKCγ signaling pathway evaluating the possibility that this might be a common pathway which contributes to these diseases.

Regulator of G protein signaling 10: Structure, expression and functions in cellular physiology and diseases

Regulator of G protein signaling 10 (RGS10) belongs to the superfamily of RGS proteins, defined by the presence of a conserved RGS domain that canonically binds and deactivates heterotrimeric G-proteins. RGS proteins act as GTPase activating proteins (GAPs), which accelerate GTP hydrolysis on the G-protein α subunits and result in termination of signaling pathways downstream of G protein-coupled receptors. RGS10 is the smallest protein of the D/R12 subfamily and selectively interacts with Gαi proteins. It is widely expressed in many cells and tissues, with the highest expression found in the brain and immune cells. RGS10 expression is transcriptionally regulated via epigenetic mechanisms. Although RGS10 lacks multiple of the defined regulatory domains found in other RGS proteins, RGS10 contains post-translational modification sites regulating its expression, localization, and function. Additionally, RGS10 is a critical protein in the regulation of physiological processes in multiple cells, where dysregulation of its expression has been implicated in various diseases including Parkinson's disease, multiple sclerosis, osteopetrosis, chemoresistant ovarian cancer and cardiac hypertrophy. This review summarizes RGS10 features and its regulatory mechanisms, and discusses the known functions of RGS10 in cellular physiology and pathogenesis of several diseases.

Top Common Differentially Expressed Genes in the Epileptogenic Nucleus of Two Strains of Rodents Susceptible to Audiogenic Seizures: WAR and GASH/Sal

The Wistar Audiogenic Rat (WAR) and the Genetic Audiogenic Seizure Hamster from Salamanca (GASH/Sal) strains are audiogenic epilepsy models, in which seizures are triggered by acoustic stimulation. These strains were developed by selective reproduction and have a genetic background with minimal or no variation. In the current study, we evaluated the transcriptome of the inferior colliculus, the epileptogenic nucleus, of both audiogenic models, in order to get insights into common molecular aspects associated to their epileptic phenotype. Based on GASH/Sal RNA-Seq and WAR microarray data, we performed a comparative analysis that includes selection and functional annotation of differentially regulated genes in each model, transcriptional evaluation by quantitative reverse transcription PCR of common genes identified in both transcriptomes and immunohistochemistry. The microarray data revealed 71 genes with differential expression in WAR, and the RNA-Seq data revealed 64 genes in GASH/Sal, showing common genes in both models. Analysis of transcripts showed that Egr3 was overexpressed in WAR and GASH/Sal after audiogenic seizures. The Npy, Rgs2, Ttr, and Abcb1a genes presented the same transcriptional profile in the WAR, being overexpressed in the naïve and stimulated WAR in relation to their controls. Npy appeared overexpressed only in the naïve GASH/Sal compared to its control, while Rgs2 and Ttr genes appeared overexpressed in naïve GASH/Sal and overexpressed after audiogenic seizure. No statistical difference was observed in the expression of Abcb1a in the GASH/Sal model. Compared to control animals, the immunohistochemical analysis of the inferior colliculus showed an increased immunoreactivity for NPY, RGS2, and TTR in both audiogenic models. Our data suggest that WAR and GASH/Sal strains have a difference in the timing of gene expression after seizure, in which GASH/Sal seems to respond more quickly. The transcriptional profile of the Npy, Rgs2, and Ttr genes under free-seizure conditions in both audiogenic models indicates an intrinsic expression already established in the strains. Our findings suggest that these genes may be causing small changes in different biological processes involved in seizure occurrence and response, and indirectly contributing to the susceptibility of the WAR and GASH/Sal models to audiogenic seizures.

RGS4 Maintains Chronic Pain Symptoms in Rodent Models

Regulator of G-protein signaling 4 (RGS4) is a potent modulator of G-protein-coupled receptor signal transduction that is expressed throughout the pain matrix. Here, we use genetic mouse models to demonstrate a role of RGS4 in the maintenance of chronic pain states in male and female mice. Using paradigms of peripheral inflammation and nerve injury, we show that the prevention of RGS4 action leads to recovery from mechanical and cold allodynia and increases the motivation for wheel running. Similarly, RGS4KO eliminates the duration of nocifensive behavior in the second phase of the formalin assay. Using the Complete Freud's Adjuvant (CFA) model of hindpaw inflammation we also demonstrate that downregulation of RGS4 in the adult ventral posterolateral thalamic nuclei promotes recovery from mechanical and cold allodynia. RNA sequencing analysis of thalamus (THL) from RGS4WT and RGS4KO mice points to many signal transduction modulators and transcription factors that are uniquely regulated in CFA-treated RGS4WT cohorts. Ingenuity pathway analysis suggests that several components of glutamatergic signaling are differentially affected by CFA treatment between RGS4WT and RGS4KO groups. Notably, Western blot analysis shows increased expression of metabotropic glutamate receptor 2 in THL synaptosomes of RGS4KO mice at time points at which they recover from mechanical allodynia. Overall, our study provides information on a novel intracellular pathway that contributes to the maintenance of chronic pain states and points to RGS4 as a potential therapeutic target.SIGNIFICANCE STATEMENT There is an imminent need for safe and efficient chronic pain medications. Regulator of G-protein signaling 4 (RGS4) is a multifunctional signal transduction protein, widely expressed in the pain matrix. Here, we demonstrate that RGS4 plays a prominent role in the maintenance of chronic pain symptoms in male and female mice. Using genetically modified mice, we show a dynamic role of RGS4 in recovery from symptoms of sensory hypersensitivity deriving from hindpaw inflammation or hindlimb nerve injury. We also demonstrate an important role of RGS4 actions in gene expression patterns induced by chronic pain states in the mouse thalamus. Our findings provide novel insight into mechanisms associated with the maintenance of chronic pain states and demonstrate that interventions in RGS4 activity promote recovery from sensory hypersensitivity symptoms.

Genetic Analysis of Rare Human Variants of Regulators of G Protein Signaling Proteins and Their Role in Human Physiology and Disease

Regulators of G protein signaling (RGS) proteins modulate the physiologic actions of many neurotransmitters, hormones, and other signaling molecules. Human RGS proteins comprise a family of 20 canonical proteins that bind directly to G protein-coupled receptors/G protein complexes to limit the lifetime of their signaling events, which regulate all aspects of cell and organ physiology. Genetic variations account for diverse human traits and individual predispositions to disease. RGS proteins contribute to many complex polygenic human traits and pathologies such as hypertension, atherosclerosis, schizophrenia, depression, addiction, cancers, and many others. Recent analysis indicates that most human diseases are due to extremely rare genetic variants. In this study, we summarize physiologic roles for RGS proteins and links to human diseases/traits and report rare variants found within each human RGS protein exome sequence derived from global population studies. Each RGS sequence is analyzed using recently described bioinformatics and proteomic tools for measures of missense tolerance ratio paired with combined annotation-dependent depletion scores, and protein post-translational modification (PTM) alignment cluster analysis. We highlight selected variants within the well-studied RGS domain that likely disrupt RGS protein functions and provide comprehensive variant and PTM data for each RGS protein for future study. We propose that rare variants in functionally sensitive regions of RGS proteins confer profound change-of-function phenotypes that may contribute, in newly appreciated ways, to complex human diseases and/or traits. This information provides investigators with a valuable database to explore variation in RGS protein function, and for targeting RGS proteins as future therapeutic targets.

Depletion of regulator-of-G-protein signaling-10 in mice exaggerates high-fat diet-induced insulin resistance and inflammation, and this effect is mitigated by dietary green tea extract

The interaction between insulin resistance and inflammation plays a central role in the development of chronic diseases, although the mechanism is not fully understood. We previously demonstrated that regulator of G-protein signaling-10 (RGS10) protein is a negative modulator of the inflammatory response in macrophages and microglia. Because inflammation is a critical component in the development of high fat diet-induced insulin resistance, in this study we investigated whether RGS10 is involved in the diet-dependent regulation of glucose tolerance and insulin sensitivity. We hypothesized that the absence of RGS10 would exaggerate high-fat diet (HFD)-induced insulin resistance and inflammation response. Our results showed that RGS10 knockout (KO) mice fed a HFD gained significantly more weight and developed severe insulin resistance compared to wild-type (WT) mice fed HFD. Furthermore, compared to WT HFD-fed mice, KO mice fed the HFD displayed inflammatory phenotypes such as decreased adipose tissue expression of the anti-inflammatory M2 markers YM1 and Fizz1 and increased expression of the proinflammatory M1 cytokine interleukin 6 in adipose and CD11b, CD68 and interleukin 1β in liver tissues. The impact of RGS10 deficiency on the exaggeration of HFD-induced insulin resistance and inflammation was ameliorated by oral consumption of green tea extract. Our results demonstrate that RGS10 is an important part of a protective mechanism involved in in regulating metabolic homeostasis by reducing inflammatory responses, which could potentially lead to an innovative new approach targeting inflammation and insulin resistance.

The antiepileptogenic effect of low-frequency stimulation on perforant path kindling involves changes in regulators of G-protein signaling in rat

G-protein coupled receptors may have a role in mediating the antiepileptogenic effect of low-frequency stimulation (LFS) on kindling acquisition. This effect is accompanied by changes at the intracellular level of cAMP. In the present study, the effect of rolipram as a phosphodiesterase inhibitor on the antiepileptogenic effect of LFS was investigated. Meanwhile, the expression of α_s- and α_i-subunit of G proteins and regulators of G-protein signaling (RGS) proteins following LFS application was measured. Male Wistar rats were kindled by perforant path stimulation in a semi-rapid kindling manner (12 stimulations per day) during a period of 6days. Application of LFS (0.1ms pulse duration at 1Hz, 200 pulses, 50-150μA, 5min after termination of daily kindling stimulations) to the perforant path retarded the kindling development and prevented the kindling-induced potentiation and kindling-induced changes in paired pulse indices in the dentate gyrus. Intra-cerebroventricular microinjection of rolipram (0.25μM) partially prevented these LFS effects. Twenty-four hours after the last kindling stimulation, the dentate gyrus was removed and changes in protein expression were measured by Western blotting. There was no significant difference in the expression of α-subunit of G_s and G_i/o proteins in different experimental groups. However, application of LFS during the kindling procedure decreased the expression RGS4 and RGS10 proteins (that reduce the activity of G_i/o) and prevented the kindling-induced decrease of RGS2 protein (which reduces the G_s activity). Therefore, it can be postulated that the G_i/o protein signaling pathways may be involved in antiepileptogenetic effect of LFS, and this is why decreasing the cAMP metabolism by rolipram attenuates this effect of LFS.

RGS2 expression predicts amyloid-β sensitivity, MCI and Alzheimer's disease: genome-wide transcriptomic profiling and bioinformatics data mining

Alzheimer's disease (AD) is the most frequent cause of dementia. Misfolded protein pathological hallmarks of AD are brain deposits of amyloid-β (Aβ) plaques and phosphorylated tau neurofibrillary tangles. However, doubts about the role of Aβ in AD pathology have been raised as Aβ is a common component of extracellular brain deposits found, also by in vivo imaging, in non-demented aged individuals. It has been suggested that some individuals are more prone to Aβ neurotoxicity and hence more likely to develop AD when aging brains start accumulating Aβ plaques. Here, we applied genome-wide transcriptomic profiling of lymphoblastoid cells lines (LCLs) from healthy individuals and AD patients for identifying genes that predict sensitivity to Aβ. Real-time PCR validation identified 3.78-fold lower expression of RGS2 (regulator of G-protein signaling 2; P=0.0085) in LCLs from healthy individuals exhibiting high vs low Aβ sensitivity. Furthermore, RGS2 showed 3.3-fold lower expression (P=0.0008) in AD LCLs compared with controls. Notably, RGS2 expression in AD LCLs correlated with the patients' cognitive function. Lower RGS2 expression levels were also discovered in published expression data sets from postmortem AD brain tissues as well as in mild cognitive impairment and AD blood samples compared with controls. In conclusion, Aβ sensitivity phenotyping followed by transcriptomic profiling and published patient data mining identified reduced peripheral and brain expression levels of RGS2, a key regulator of G-protein-coupled receptor signaling and neuronal plasticity. RGS2 is suggested as a novel AD biomarker (alongside other genes) toward early AD detection and future disease modifying therapeutics.

Genetic mechanisms of electroconvulsive therapy response in depression

Electroconvulsive therapy (ECT) is known to be one of the most effective treatments for managing depression and other severe mental illnesses. Nevertheless, the exact mechanisms underlying response to ECT remain uncertain. This mini-review presents clinical findings regarding the role of genetic factors in the aetiology of the ECT response. Studies on the role of variation in the catechol-O-methyltransferase (COMT) gene; other dopamine-, serotonin-, and G-protein-related genes; brain-derived neurotrophic factor (BDNF); apolipoprotein E (APOE); angiotensin I-converting enzyme (ACE) and vascular endothelial growth factor (VEGF) genes in mediating response to ECT are summarized. The existing data support the notion that some genetic factors-particularly the functional COMT val158met polymorphism-may play a role in the magnitude of clinical response to ECT, and thus could serve as potential biomarkers for future personalized treatment approaches. However, much of the work to date is preliminary, and large-scale confirmatory studies are still needed. Copyright © 2016 John Wiley & Sons, Ltd.

Adenosine Receptors Differentially Regulate the Expression of Regulators of G-Protein Signalling (RGS) 2, 3 and 4 in Astrocyte-Like Cells

The “regulators of g-protein signalling” (RGS) comprise a large family of proteins that limit by virtue of their GTPase accelerating protein domain the signal transduction of G-protein coupled receptors. RGS proteins have been implicated in various neuropsychiatric diseases such as schizophrenia, drug abuse, depression and anxiety and aggressive behaviour. Since conditions associated with a large increase of adenosine in the brain such as seizures or ischemia were reported to modify the expression of some RGS proteins we hypothesized that adenosine might regulate RGS expression in neural cells. We measured the expression of RGS-2,-3, and -4 in both transformed glia cells (human U373 MG astrocytoma cells) and in primary rat astrocyte cultures stimulated with adenosine agonists. Expression of RGS-2 mRNA as well as RGS2 protein was increased up to 30-fold by adenosine agonists in astrocytes. The order of potency of agonists and the blockade by the adenosine A2B-antagonist MRS1706 indicated that this effect was largely mediated by adenosine A2B receptors. However, a smaller effect was observed due to activation of adenosine A2A receptors. In astrocytoma cells adenosine agonists elicited an increase in RGS-2 expression solely mediated by A2B receptors. Expression of RGS-3 was inhibited by adenosine agonists in both astrocytoma cells and astrocytes. However while this effect was mediated by A2B receptors in astrocytoma cells it was mediated by A2A receptors in astrocytes as assessed by the order of potency of agonists and selective blockade by the specific antagonists MRS1706 and ZM241385 respectively. RGS-4 expression was inhibited in astrocytoma cells but enhanced in astrocytes by adenosine agonists.

Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling

Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.

Inhibition of HDAC1 and DNMT1 modulate RGS10 expression and decrease ovarian cancer chemoresistance

RGS10 is an important regulator of cell survival and chemoresistance in ovarian cancer. We recently showed that RGS10 transcript expression is suppressed during acquired chemoresistance in ovarian cancer. The suppression of RGS10 is due to DNA hypermethylation and histone deacetylation, two important mechanisms that contribute to silencing of tumor suppressor genes during cancer progression. Here, we fully investigate the molecular mechanisms of epigenetic silencing of RGS10 expression in chemoresistant A2780-AD ovarian cancer cells. We identify two important epigenetic regulators, HDAC1 and DNMT1, that exhibit aberrant association with RGS10 promoters in chemoresistant ovarian cancer cells. Knockdown of HDAC1 or DNMT1 expression, and pharmacological inhibition of DNMT or HDAC enzymatic activity, significantly increases RGS10 expression and cisplatin-mediated cell death. Finally, DNMT1 knock down also decreases HDAC1 binding to the RGS10 promoter in chemoresistant cells, suggesting HDAC1 recruitment to RGS10 promoters requires DNMT1 activity. Our results suggest that HDAC1 and DNMT1 contribute to the suppression of RGS10 during acquired chemoresistance and support inhibition of HDAC1 and DNMT1 as an adjuvant therapeutic approach to overcome ovarian cancer chemoresistance.

Electroconvulsive seizures activate anorexigenic signals in the ventromedial nuclei of the hypothalamus

The ventromedial nucleus of the hypothalamus (VMH) plays an important role in feeding and energy homeostasis. Electroconvulsive seizure (ECS) therapy is highly effective in the treatment of several psychiatric diseases, including depression, but may also have beneficial effects in other neurological diseases. Although it has been reported that the neurons of the VMH are strongly activated by ECS stimulation, the specific effects of ECS in this hypothalamic subnucleus remain unknown. To address this issue, we investigated the changes in gene expression in microdissected-VMH samples in response to ECS in mice, and examined the behavioral effects of ECS on feeding behavior. ECS significantly induced the expression of immediate-early genes such as Fos, Fosb, and Jun, as well as Bdnf, Adcyap1, Hrh1, and Crhr2 in the VMH. Given that signals of these gene products are suggested to have anorexigenic roles in the VMH, we also examined the effect of ECS on food intake and body weight. Repeated ECS had a suppressive effect on food intake and body weight gain under both regular and high-fat diet conditions. Furthermore, gold-thioglucose-induced hypothalamic lesions, including the VMH and the arcuate nucleus, abolished the anorexigenic effects of ECS, indicating the requirement for the activation of the hypothalamus. Our data show an effect of ECS on increased expression of anorexigenic factors in the VMH, and suggest a role in the regulation of energy homeostasis by ECS.

Brain RGS4 and RGS10 protein expression in schizophrenia and depression. Effect of drug treatment

RATIONALE

Regulator of G-protein signaling (RGS) proteins, RGS4 and RGS10, may be involved in the pathophysiology of schizophrenia. RGS4 has attracted special interest since the reports of genetic association between SNPs in RGS4 and schizophrenia. However, there is no information about the subcellular distribution of RGS4 and RGS10 proteins in psychiatric disorders.

OBJECTIVES

Plasma membrane RGS4 and cytosolic RGS10 protein immunoreactivity in prefrontal cortex from schizophrenic subjects (n = 25), non-diagnosed suicides (n = 13), and control subjects (n = 35), matched by age, gender, and postmortem delay, was analyzed by western blot. A second group of depressed subjects (n = 25) and control subjects (n = 25) was evaluated. The effect of the antipsychotic or antidepressant treatments was also assessed.

RESULTS

No significant differences in plasma membrane RGS4 and cytosolic RGS10 protein expression were observed between schizophrenic subjects, non-diagnosed suicides, and control subjects. However, RGS4 immunoreactivity was significantly higher (Δ = 33 ± 10 %, p < 0.05) in the antipsychotic-treated subgroup (n = 12) than in the antipsychotic-free subgroup (n = 13). Immunodensities of plasma membrane RGS4 and cytosolic RGS10 proteins did not differ between depressed and matched control subjects.

CONCLUSIONS

Expression of RGS4 and RGS10 proteins at their predominant subcellular location was studied in the postmortem brain of subjects with psychiatric disorders. The results suggest unaltered membrane RGS4 and cytosolic RGS10 proteins levels in schizophrenia and major depression. Antipsychotic treatment seems to increase membrane RGS4 immunoreactivity. Further studies are needed to elucidate RGS4 and RGS10 functional status.

Layer-specific CREB target gene induction in human neocortical epilepsy

Epilepsy is a disorder of recurrent seizures that affects 1% of the population. To understand why some areas of cerebral cortex produce seizures and others do not, we identified differentially expressed genes in human epileptic neocortex compared with nearby regions that did not produce seizures. The transcriptome that emerged strongly implicates MAPK signaling and CREB-dependent transcription, with 74% of differentially expressed genes containing a cAMP response element (CRE) in their proximal promoter, more than half of which are conserved. Despite the absence of recent seizures in these patients, epileptic brain regions prone to seizures showed persistent activation of ERK and CREB. Persistent CREB activation was directly linked to CREB-dependent gene transcription by chromatin immunoprecipitation that showed phosphorylated CREB constitutively associated with the proximal promoters of many of the induced target genes involved in neuronal signaling, excitability, and synaptic plasticity. A distinct spatial pattern of ERK activation was seen in superficial axodendritic processes of epileptic neocortex that colocalized with both CREB phosphorylation and CREB target gene induction in well demarcated populations of layer 2/3 neurons. These same neuronal lamina showed a marked increase in synaptic density. The findings generated in this study generate a robust and spatially restricted pattern of epileptic biomarkers and associated synaptic changes that could lead to new mechanistic insights and potential therapeutic targets for human epilepsy.

RGS10 exerts a neuroprotective role through the PKA/c-AMP response-element (CREB) pathway in dopaminergic neuron-like cells

Regulator of G-protein signaling-10 (RGS10) is a GTPase activating protein for Gαi/q/z subunits that is highly expressed in the immune system and in a broad range of brain regions including the hippocampus, striatum, dorsal raphe, and ventral midbrain. Previously, we reported that RGS10-null mice display increased vulnerability to chronic systemic inflammation-induced degeneration of nigral dopaminergic (DA) neurons. Given that RGS10 is expressed in DA neurons, we investigated the extent to which RGS10 regulates cell survival under conditions of inflammatory stress. Because of the inherent limitations associated with use of primary DA neurons for biochemical analyses, we employed a well-characterized ventral mesencephalon DA neuroblastoma cell line (MN9D) for our studies. We found that stable over-expression of RGS10 rendered them resistant to TNF-induced cytotoxicity; whereas MN9D cells expressing mutant RGS10-S168A (which is resistant to phosphorylation by protein kinase A at a serine residue that promotes its nuclear translocation) showed similar sensitivity to TNF as the parental MN9D cells. Using biochemical and pharmacologic approaches, we identified protein kinase A and the downstream phospho-cAMP response element-binding signaling pathway (and ruled out ERK 1/2, JNK, and NFkB) as key mediators of the neuroprotective effect of RGS10 against inflammatory stress.

Structure, function, and localization of Gβ5-RGS complexes

Members of the R7 subfamily of regulator of G protein signaling (RGS) proteins (RGS6, 7, 9, and 11) exist as heterodimers with the G protein beta subunit Gβ5. These protein complexes are only found in neurons and are defined by the presence of three domains: DEP/DHEX, Gβ5/GGL, and RGS. This article summarizes published work in the following areas: (1) the functional significance of structural organization of Gβ5-R7 complexes, (2) regional distribution of Gβ5-R7 in the nervous system and regulation of R7 family expression, (3) subcellular localization of Gβ5-R7 complexes, and (4) novel binding partners of Gβ5-R7 proteins. The review points out some contradictions between observations made by different research groups and highlights the importance of using alternative experimental approaches to obtain conclusive information about Gβ5-R7 function in vivo.

Regulation of hippocampal and behavioral excitability by cyclin-dependent kinase 5

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase that has been implicated in learning, synaptic plasticity, neurotransmission, and numerous neurological disorders. We previously showed that conditional loss of Cdk5 in adult mice enhanced hippocampal learning and plasticity via modulation of calpain-mediated N-methyl-D-aspartic acid receptor (NMDAR) degradation. In the present study, we characterize the enhanced synaptic plasticity and examine the effects of long-term Cdk5 loss on hippocampal excitability in adult mice. Field excitatory post-synaptic potentials (fEPSPs) from the Schaffer collateral CA1 subregion of the hippocampus (SC/CA1) reveal that loss of Cdk5 altered theta burst topography and enhanced post-tetanic potentiation. Since Cdk5 governs NMDAR NR2B subunit levels, we investigated the effects of long-term Cdk5 knockout on hippocampal neuronal excitability by measuring NMDAR-mediated fEPSP magnitudes and population-spike thresholds. Long-term loss of Cdk5 led to increased Mg²⁺-sensitive potentials and a lower threshold for epileptiform activity and seizures. Biochemical analyses were performed to better understand the role of Cdk5 in seizures. Induced-seizures in wild-type animals led to elevated amounts of p25, the Cdk5-activating cofactor. Long-term, but not acute, loss of Cdk5 led to decreased p25 levels, suggesting that Cdk5/p25 may be activated as a homeostatic mechanism to attenuate epileptiform activity. These findings indicate that Cdk5 regulates synaptic plasticity, controls neuronal and behavioral stimulus-induced excitability and may be a novel pharmacological target for cognitive and anticonvulsant therapies.

PLC-beta1 knockout mice as a model of disrupted cortical development and plasticity: behavioral endophenotypes and dysregulation of RGS4 gene expression

The complexity of the genetics underlying schizophrenia is highlighted by the multitude of molecular pathways that have been reported to be disrupted in the disorder including muscarinic, serotonergic, and glutamatergic signaling systems. It is of interest, therefore, that phospholipase C-beta1 (PLC-beta1) acts as a point of convergence for these pathways during cortical development and plasticity. These signaling pathways, furthermore, are susceptible to modulation by RGS4, one of the more promising candidate genes for schizophrenia. PLC-beta1 knockout mice were behaviorally assessed on tests including fear conditioning, elevated plus maze, and the Y maze. In situ hybridization was used to assess RGS4 expression. We found that PLC-beta1 knockout mice display abnormal anxiety profiles on some, but not all measures assessed, including decreased anxiety on the elevated plus maze. We also show memory impairment and a complete absence of acquisition of hippocampal-dependent fear conditioning. Furthermore, at a molecular level, we demonstrate dramatic changes in expression of RGS4 mRNA in selective regions of the PLC-beta1 knockout mouse brain, particularly the CA1 region of the hippocampus. These results validate the utility of the PLC-beta1 knockout mouse as a model of schizophrenia, including molecular and cellular evidence for disrupted cortical maturation and associated behavioral endophenotypes.

Regulation of psychostimulant-induced signaling and gene expression in the striatum

Amphetamine (AMPH) and cocaine are indirect dopamine agonists that activate multiple signaling cascades in the striatum. Each cascade has a different subcellular location and duration of action that depend on the strength of the drug stimulus. In addition to activating D1 dopamine-Gs-coupled-protein kinase A signaling, acute psychostimulant administration activates extracellular-regulated kinase transiently in striatal cells; conversely, inhibition of extracellular-regulated kinase phosphorylation decreases the ability of psychostimulants to elevate locomotor behavior and opioid peptide gene expression. Moreover, a drug challenge in rats with a drug history augments and prolongs striatal extracellular-regulated kinase phosphorylation, possibly contributing to behavioral sensitization. In contrast, AMPH activates phosphoinositide-3 kinase substrates, like protein kinase B/Akt, only in the nuclei of striatal cells but this transient increase induced by AMPH is followed by a delayed decrease in protein kinase B/Akt phosphorylation whether or not the rats have a drug history, suggesting that the phosphoinositide-3 kinase pathway is not essential for AMPH-induced behavioral sensitization. Chronic AMPH or cocaine also alters the regulation of inhibitory G protein-coupled receptors in the striatum, as evident by a prolonged decrease in the level of regulator of G protein signaling 4 after non-contingent or contingent (self-administered) drug exposure. This decrease is exacerbated in behaviorally sensitized rats and reversed by re-exposure to a cocaine-paired environment. A decrease in regulator of G protein signaling 4 levels may weaken its interactions with metabotropic glutamate receptor 5, Galphaq, and phospholipase C beta that may enhance drug-induced signaling. Alteration of these protein-protein interactions suggests that the striatum responds to psychostimulants with a complex molecular repertoire that both modulates psychomotor effects and leads to long-term neuroadaptations.

R4 RGS proteins: regulation of G-protein signaling and beyond

The regulators of G-protein signaling (RGS) proteins were initially characterized as inhibitors of signal transduction cascades initiated by G-protein-coupled receptors (GPCR) because of their ability to increase the intrinsic GTPase activity of heterotrimeric G proteins. This GTPase accelerating protein (GAP) activity enhances G protein deactivation and promotes desensitization. However, in addition to this signature trait, emerging data have revealed an expanding network of proteins, lipids, and ions that interact with RGS proteins and confer additional regulatory functions. This review highlights recent advances in our understanding of the physiological functions of one subfamily of RGS proteins with a high degree of homology (B/R4) gleaned from recent studies of knockout mice or cells with reduced RGS expression. We also discuss some of the newly appreciated interactions of RGS proteins with cellular factors that suggest RGS control of several components of G-protein-mediated pathways, as well as a diverse array of non-GPCR-mediated biological responses.

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.

Leptin receptor signaling in midbrain dopamine neurons regulates feeding

The leptin hormone is critical for normal food intake and metabolism. While leptin receptor (Lepr) function has been well studied in the hypothalamus, the functional relevance of Lepr expression in the ventral tegmental area (VTA) has not been investigated. The VTA contains dopamine neurons that are important in modulating motivated behavior, addiction, and reward. Here, we show that VTA dopamine neurons express Lepr mRNA and respond to leptin with activation of an intracellular JAK-STAT pathway and a reduction in firing rate. Direct administration of leptin to the VTA caused decreased food intake while long-term RNAi-mediated knockdown of Lepr in the VTA led to increased food intake, locomotor activity, and sensitivity to highly palatable food. These data support a critical role for VTA Lepr in regulating feeding behavior and provide functional evidence for direct action of a peripheral metabolic signal on VTA dopamine neurons.

RGS3 and RGS4 Differentially Associate with G Protein-coupled Receptor-Kir3 Channel Signaling Complexes Revealing Two Modes of RGS Modulation

RGS3 and RGS4 are GTPase-activating proteins expressed in the brain and heart that accelerate the termination of G(i/o)- and G(q)-mediated signaling. We report here the determinants mediating selective association of RGS4 with several G protein-coupled receptors (GPCRs) that form macromolecular complexes with neuronal G protein-gated inwardly rectifying potassium (Kir3 or GIRK) channels. Kir3 channels are instrumental in regulating neuronal firing in the central and peripheral nervous system and pacemaker activity in the heart. By using an epitope-tagged degradation-resistant RGS4 mutant, RGS4(C2V), immunoprecipitation of several hemagglutinin-tagged G(i/o)-coupled and G(q)-coupled receptors expressed in Chinese hamster ovary (CHO-K1) cells readily co-precipitated both Kir3.1/Kir3.2a channels and RGS4(C2V). In contrast to RGS4(C2V), the closely related and functionally active RGS3 "short" isoform (RGS3s) did not interact with any of the GPCR-Kir3 channel complexes examined. Deletion and chimeric RGS constructs indicate both the N-terminal domain and the RGS domain of RGS4(C2V) are necessary for association with m2 receptor-Kir3.1/Kir3.2a channel complexes, where the GPCR was found to be the major target for RGS4(C2V) interaction. The functional impact of RGS4(C2V) "precoupling" to the GPCR-Kir3 channel complex versus RGS3s "collision coupling" was a 100-fold greater potency in the acceleration of G protein-dependent Kir3 channel-gating kinetics with no attenuation in current amplitude. These findings demonstrate that RGS4, a highly regulated modulator and susceptibility gene for schizophrenia, can directly associate with multiple GPCR-Kir3 channel complexes and may affect a wide range of neurotransmitter-mediated inhibitory and excitatory events in the nervous and cardiovascular systems.

RGS expression rate-limits recovery of rod photoresponses

Signaling through G protein-coupled receptors (GPCRs) underlies many cellular processes, yet it is not known which molecules determine the duration of signaling in intact cells. Two candidates are G protein-coupled receptor kinases (GRKs) and Regulators of G protein signaling (RGSs), deactivation enzymes for GPCRs and G proteins, respectively. Here we investigate whether GRK or RGS governs the overall rate of recovery of the light response in mammalian rod photoreceptors, a model system for studying GPCR signaling. We show that overexpression of rhodopsin kinase (GRK1) increases phosphorylation of the GPCR rhodopsin but has no effect on photoresponse recovery. In contrast, overexpression of the photoreceptor RGS complex (RGS9-1.Gbeta5L.R9AP) dramatically accelerates response recovery. Our results show that G protein deactivation is normally at least 2.5 times slower than rhodopsin deactivation, resolving a long-standing controversy concerning the mechanism underlying the recovery of rod visual transduction.

Genetic or pharmacological inactivation of the dopamine D 1 receptor differentially alters the expression of regulator of G‐protein signalling (Rgs) transcripts

Dysregulation of dopamine (DA) receptor signalling induces specific changes in behaviour, neuronal circuitry and gene expression in the mammalian forebrain. In order to better understand signalling adaptations at the molecular level, we used high-density oligonucleotide microarrays (Codelink Mouse 20K) to define alterations in the expression of transcripts encoding regulator of G-protein coupled receptor signalling in dopamine D1 receptor knockout mice (Drd1a-KO). Regulator of G-protein signalling (Rgs) 2, Rgs4, and Rgs9 were significantly decreased in the striatum (STR) of Drd1a-KO mice. These changes were confirmed by in situ hybridization, and were also observed in the nucleus accumbens (NAc). In contrast, analysis of the medial frontal cortex (MFC) revealed a significant decrease in Rgs17 expression exclusively, and a modest up-regulation of Rgs5 transcript. The expression of these gene products were not significantly altered in the dopamine-poor visual cortex (VC). The Drd1a-KO mouse, and a rabbit model of in utero cocaine exposure, in which D1R signalling is permanently reduced, possess analogous morphological and functional alterations in dopamine-modulated brain circuits; thus we also examined long-lasting changes in RGS transcript expression following prenatal exposure to cocaine. In sharp contrast to the Drd1a-KO, Rgs2 and Rgs4 were unchanged, and Rgs9 and Rgs17 transcripts were increased in prenatal cocaine-exposed progeny. These data suggest that an absolute absence of D1R signalling (Drd1a-KO) and hypomorphic D1R signalling (prenatal cocaine) produce common alterations in neuronal morphology, but distinct outcomes in molecular neuroadaptations.

Ischemia-induced increase in RGS7 mRNA expression in gerbil hippocampus

The present study investigated the changes in the expression of regulators of G-protein-coupled signaling proteins RGS2, 7 and 8 in gerbil hippocampus to better understand alterations of G-protein-coupled receptors signaling after cerebral ischemia. In situ hybridization revealed a transient, robust early increase in RGS7 mRNA levels in the dentate gyrus after ischemia. RGS8 mRNA expression started to increase at a later time point in the CA3 region but no changes were found for RGS2. Our results show a subtype-, time-, and subregion-specific regulation in mRNA expression of RGS proteins after cerebral ischemia in gerbil hippocampus.

RGS2 promotes formation of neurites by stimulating microtubule polymerization

Regulator of G-protein signaling (RGS) proteins interact with alpha subunits of heterotrimeric G-proteins via the RGS domain and attenuate their activity by accelerating GTPase activity. RGS2, a member of the RGS family, regulates synaptic development via hereto unknown mechanism. In this study, we found that RGS2 directly interacted with tubulin via a short region at the N-terminus: amino acids 41-60. RGS2 enhanced microtubule polymerization in vitro, and the tubulin binding region was necessary and sufficient for this activity. In Vero cells, polymerization of microtubule was stimulated when peptides containing the tubulin binding region were microinjected. Immunocytochemical analysis showed that endogenous RGS2 was localized at the termini of neurites in differentiated PC12 cells. Over-expression of RGS2 enhanced the nerve growth factor-induced neurite outgrowth in PC12 cells, while specific knock-down of endogenous RGS2 suppressed the neurite outgrowth. These findings demonstrate that RGS2 contributes to the neuronal cell differentiation via regulation of microtubule dynamics.

The vertebrate phototransduction cascade: amplification and termination mechanisms

The biochemical cascade which transduces light into a neuronal signal in retinal photoreceptors is a heterotrimeric GTP-binding protein (G protein) signaling pathway called phototransduction. Works from psychophysicists, electrophysiologists, biochemists, and geneticists over several decades have come together to shape our understanding of how photon absorption leads to photoreceptor membrane hyperpolarization. The insights of phototransduction provide the foundation for a mechanistic account of signaling from many other G protein-coupled receptors (GPCR) found throughout nature. The application of reverse genetic techniques has strengthened many historic findings and helped to describe this pathway at greater molecular details. However, many important questions remain to be answered.

Acute amphetamine down-regulates RGS4 mRNA and protein expression in rat forebrain: distinct roles of D1and D2dopamine receptors

Administration of psychostimulants modulates mRNA of several regulators of guanine nucleotide-binding protein signaling (RGSs) proteins in the brain. In the present study, the regulation of amphetamine-induced decrease of RGS4 expression in the rat forebrain was evaluated. RGS4 mRNA was reduced by amphetamine in an inverse, dose-dependent manner. The lowest dose (2.5 mg/kg) decreased RGS4 mRNA in caudate putamen for up to 6 h after injection whereas the decrease in several frontal cortical areas was detected at 3 h only. Analysis of RGS4 immunoreactivity by western blotting revealed a decrease 3 h after amphetamine solely in the caudate putamen. Systemic administration of D(1) (SCH23390) or D(2) (eticlopride) receptor antagonists blocked amphetamine-induced locomotion but amphetamine augmented both the SCH23390-induced increase and the eticlopride-induced decrease in RGS4 mRNA in the caudate putamen. Further, the down-regulation of RGS4 immunoreactivity by eticlopride was robust whereas the effect of SCH23390 was blunted as compared with its effect on mRNA. These data suggest that, by decreasing RGS4 expression in the caudate putamen via D(1) receptors, acute amphetamine could disinhibit RGS4-sensitive guanine nucleotide-binding protein alpha-subunit i- and/or q-coupled signaling pathways and favor mechanisms that counterbalance D(1) receptor stimulation.

Comprehensive regional and temporal gene expression profiling of the rat brain during the first 24 h after experimental stroke identifies dynamic ischemia-induced gene expression patterns, and reveals a biphasic activation of genes in surviving tissue

In order to identify biological processes relevant for cell death and survival in the brain following stroke, the postischemic brain transcriptome was studied by a large-scale cDNA array analysis of three peri-infarct brain regions at eight time points during the first 24 h of reperfusion following middle cerebral artery occlusion in the rat. K-means cluster analysis revealed two distinct biphasic gene expression patterns that contained 44 genes (including 18 immediate early genes), involved in cell signaling and plasticity (i.e. MAP2K7, Sprouty2, Irs-2, Homer1, GPRC5B, Grasp). The first gene induction phase occurred at 0-3 h of reperfusion, and the second at 9-15 h, and was validated by in situ hybridization. Four gene clusters displayed a progressive increase in expression over time and included 50 genes linked to cell motility, lipid synthesis and trafficking (i.e. ApoD, NPC1, G3P-dehydrogenase1, and Choline kinase) or cell death-regulating genes such as mitochondrial CLIC. We conclude that a biphasic transcriptional up-regulation of the brain-derived neurotrophic factor (BDNF)-G-protein coupled receptor (GPCR)-mitogen-activated protein (MAP) kinase signaling pathways occurs in surviving tissue, concomitant with a progressive and persistent activation of cell proliferation signifying tissue regeneration, which provide the means for cell survival and postischemic brain plasticity.

Regional alterations in RGS4 protein in schizophrenia

The regulator of G protein signaling (RGS) molecules are a class of proteins that modulate the signaling activity of G-protein coupled receptors. Regulator of G protein signaling 4 (RGS4) is of particular interest in schizophrenia since it is associated with the dopamine (DA) receptor, its expression is altered in affected CNS tissue, and polymorphisms in the RGS4 gene are being examined as risk factors for the disease (Morris et al.2004, Am J Med Genet B Neuropsychiatr Genet 125:50-53; Prasad et al.2005, Mol Psychiatry 10:213-219; Williams et al.2004, Biol Psychiatry 55:192-195). To further test for the involvement of RGS4 expression in schizophrenia, we examined a selection of different cortical and subcortical regions in human brain for alterations in RGS4 mRNA and protein expression. To evaluate the effect of antipsychotic medication on RGS4 expression levels, we compared a subset of treated and untreated cases that were off antipsychotic medication for at least 3 months prior to death. We report a significant decrease in RGS4 mRNA levels in the cingulate gyrus, superior frontal gyrus, and the insular cortex of all schizophrenia cases when compared with controls. A decrease in RGS4 mRNA was also observed in the caudate, but only in the medicated schizophrenia cases. Measurement of protein levels using Western blot demonstrated that RGS4 protein is decreased in the frontal cortex of schizophrenia cases.

Bilateral control of brain activity by dopamine D1 receptors: evidence from induction patterns of regulator of G protein signaling 2 and c-fos mRNA in D1-challenged hemiparkinsonian rats

Recent reports show that striatal dopamine D1-type receptors from one side of the normal rat brain can control brain activity (as measured by c-fos induction) on both sides of the brain. However, this phenomenon has not yet been studied in the presence of sensitized dopamine D1-type receptors. Here we address this issue by investigating the extent to which dopamine D1-type receptors control brain activation in rats with unilaterally sensitized dopamine D1-type receptors. Gene induction assays were used to identify activated regions from midbrain to forebrain in unilaterally 6-hydroxydopamine lesioned (hemiparkinsonian) rats challenged with the full dopamine D1-type agonist SKF82958 (3 mg/kg, 0.5 and 2 h). The genes used are c-fos, the proven neuronal activity marker, and Regulator of G protein Signaling 2, a gene we propose as a marker of signaling homeostasis. SKF82958-mediated induction of both genes is greatly enhanced in hemiparkinsonian rats compared with shams, in both the lesioned and the intact hemisphere. For example, in the denervated caudate-putamen at 2 h postinjection, this enhancement is more than 80-fold for c-fos and up to 20-fold for Regulator of G protein Signaling 2; for the intact side this is 35-fold for c-fos and 27-fold for Regulator of G protein Signaling 2. Cortical induction of c-fos and Regulator of G protein Signaling 2 was generalized to most neocortical regions and was essentially equivalent in both the denervated and intact hemispheres. Interestingly, hippocampal structures also showed strong bilateral induction of both genes. This overall pattern of brain activation can be accounted for by the basal-ganglia thalamocortical and hippocampal circuits which both contain hemisphere-crossing connections and which can be initially activated in the lesioned hemisphere. Some regions, such as the intact striatum or the CA1 region, showed relatively low c-fos induction and relatively high Regulator of G protein Signaling 2 induction, possibly indicating that these regions are engaged in unusually strong signaling regulation activities. Our results show that, besides basal ganglia-thalamocortical circuits, dopamine D1-type-mediated brain activation in hemiparkinsonian rats also involves hippocampal circuits.

MK-801 alters RGS2 levels and adenylyl cyclase sensitivity in the rat striatum

The present report examines the effects of acute NMDA antagonism on Regulator of G Protein Signaling 2 (RGS2) expression and adenylyl cyclase sensitivity in the rat striatum. MK-801 and phencyclidine rapidly down-regulate RGS2 mRNA. The down-regulation of RGS2 by MK-801 was dose dependent and transient. Because previous reports showed that RGS2 attenuates activity of adenylyl cyclase, RGS2 protein level and sensitivity of adenylyl cyclase to forskolin was tested 2 h after administration of MK-801 (1 mg/kg). In striatal membranes of these rats, RGS2 protein level was 17% lower and forskolin-stimulated cAMP production 38% higher than in controls. These findings reveal a cross-talk between NMDA receptors and adenylyl cyclase and suggest a general cross-talk mechanism by which RGS proteins transcriptionally regulated by ionotropic receptors can alter signaling properties of metabotropic receptors.

Expression of neural RGS-R7 and Gbeta5 Proteins in Response to Acute and Chronic Morphine

The R7 subfamily of regulators of G-protein signaling (RGS) proteins (RGS6, RGS7, RGS9-2, and RGS11), and its binding protein Gbeta5, are found in neural structures of mouse brain. A single intracerebroventricular priming dose of 10 nmol morphine gave rise to acute tolerance to the analgesic effects of successive identical test doses of the opioid. At 2 h after administering the acute opioid, RGS7 mRNA levels in the striatum plus those of RGS9-2 in the striatum and thalamus were increased, whereas RGS9-2 and RGS11 mRNA were reduced in the cortex. Similar but attenuated RGS-R7 mRNA changes persisted 24 h after acute morphine administration. No changes in Gbeta5 mRNA levels were observed. At 2 days after commencing sustained morphine treatment, the levels of mRNA for RGS7, RGS9-2, RGS11, and Gbeta5 increased in most of the brain structures studied (striatum, thalamus, periaqueductal gray matter (PAG), and cortex). In these morphine tolerant-dependent mice, the greater changes were found for RGS9-2 in the thalamus (>500%) and PAG (>200%). In post-dependent mice, the increases in RGS-R7 and Gbeta5 mRNA still persisted in the PAG and striatum at 8 and 16 days after starting the chronic opioid treatment. The raised mRNA levels promoted by chronic, but not by acute, morphine, were accompanied by increases in the encoded proteins. This is probably a result of the costabilization of the RGS-R7 and Gbeta5 proteins forming heterodimers. Opioid-induced adaptations of RGS-R7 and Gbeta5 genes may regulate the severity of morphine-induced tolerance/dependence and the duration of the post-dependent period, helping to recover the normal response.

Novel missense polymorphism in the regulator of G-protein signaling 10 gene: analysis of association with schizophrenia

Dysfunction of neuronal signal transduction via G-protein has previously been speculated to be involved in the pathophysiology of schizophrenia. Regulator of G-protein signaling (RGS) is a protein that acts as a GTPase-activator for Galpha protein. A total of 33 Japanese patients with schizophrenia were screened for mutations in the coding region of the RGS10 gene, and a novel missense polymorphism (Val38Met) in the RGS domain was detected. A case-control study did not reveal a significant association between this polymorphism and schizophrenia. The results do not provide evidence that the RGS10 gene is involved in biological vulnerability to schizophrenia.

Dopamine receptor-mediated regulation of RGS2 and RGS4 mRNA differentially depends on ascending dopamine projections and time

RGS2 and RGS4 mRNAs are regulated in the rat striatum by dopaminergic agents. The present study further characterizes this regulation in three experiments. First, dopamine type 1 (receptor) (D1)- and dopamine type 2 (receptor) (D2)-mediated regulator of G-protein signalling (RGS) gene regulation was investigated in animals with deleted ascending dopaminergic pathways. We showed that RGS2 expression is controlled by D1 receptors either by direct action on D1 receptors or indirectly by presynaptic D2 receptors. Conversely, RGS4 gene expression is independent of presynaptic D2 receptors. Second, the study of colocalization between RGS2 or RGS4 and D1 or D2 by double labelling in situ hybridization histochemistry revealed broad expression of RGS2 and RGS4 mRNA in striatal subpopulations with colocalization of RGS2 and RGS4 with both D1 and D2 receptors. Finally, to test how far their gene regulation is temporally concerted, changes in RGS2 and RGS4 mRNA levels were measured in parallel with receptor occupancy by specific dopaminergic drugs at different time-points. RGS2 was rapidly/transiently up-regulated by the D1 agonist SKF82958 and the D2 antagonist haloperidol (peak at 0.5 h) and down-regulated by the D1 antagonist SCH23390 and the D2 agonist quinpirole (trough at 1 and 2 h). RGS4 showed a delayed/transient up-regulation with SCH23390 and quinpirole (peak at 4 and 2 h) and down-regulation with haloperidol (trough at 8 h). Depending on the drug used, the degree of receptor occupancy did (D1 agonist and RGS2) or did not (D2 antagonist and RGS2) run parallel to RGS gene expression changes, indicating that certain drug effects are direct and others indirect. The precise control of RGS2 and RGS4 expression by dopamine receptors pleads in favour of their potential contribution to the fine-tuning of D1 and D2 receptor signalling cascades.

Selective expression of regulators of G-protein signaling (RGS) in the human central nervous system

The human tissue distribution of the nineteen known human regulators of G-protein signaling (RGS) is described. Measurement of RGS mRNA levels in human brain and in nine peripheral tissues revealed striking tissue preferences in gene expression. Five RGS members were identified with enriched expression in brain. RGS4, RGS7, RGS8, RGS11 and RGS17 were all significantly expressed in striatal regions including the nucleus accumbens and putamen. RGS4 had the highest measured levels of mRNA expression and was highly enriched in the gyrus of the cortex and in the parahippocampus. RGS7 and RGS17 had overlapping distribution profiles and were both noticeably enriched in the cerebellum. Several RGS family members showed high expression in peripheral tissues. RGS5 was preferentially expressed in heart, and RGS1, RGS13, RGS18 and GAIP were predominately expressed in lymphocytes. RGS1 was also highly enriched in the lung, as was RGS2 and RGS16. Five family members, RGS3, RGS9, RGS10, RGS 12 and RGS14 had a broad and overlapping mRNA distribution. These results suggest roles of the individual RGS members in a diversity of functions in humans and support a role of several RGS members in the regulation of central nervous system function via modulation of signaling by G-protein coupled receptors.

Regional, cellular, and subcellular localization of RGS10 in rodent brain

The regulator of G protein signaling type 10 (RGS10) modulates Galphai/o signaling by means of its GTPase accelerating activity and is abundantly expressed in brain and in immune tissues. To elucidate RGS10 function in the nervous system, we mapped RGS10 protein in rat and mouse brain using light microscopic (LM) and electron microscopic (EM) immunohistochemical techniques. The LM showed that RGS10-like immunoreactivity (LIR) labels all cellular subcompartments of neurons and microglia, including their nuclei. There were several differences between RGS10-LIR distributions in rat and mouse, the most striking of which were the far denser immunoreactivity in rat dentate gyrus and dorsal raphe. The EM analysis corroborated and extended our findings from LM. Thus, EM confirmed the presence of dense RGS10-LIR in the euchromatin compartment of nuclei. The EM analysis also resolved dense staining on terminals at symmetric synapses onto pyramidal cell somata. Dual immunofluorescence showed that forebrain interneurons densely labeled with RGS10-LIR partially colocalized with parvalbumin-LIR. Dual-labeling histochemistry in caudoputamen demonstrated that densely labeled striatal cells were biased to the indirect-projecting output pathway. Dual-labeling immunofluorescence also showed that densely labeled RGS10-LIR cells in the dentate gyrus subgranular zone were not proliferating but that newly born cells could differentiate to express RGS10-LIR. Taken together, these data support a role for RGS10 in diverse processes that include modulation of pre- and postsynaptic G-protein signaling. Moreover, enrichment of RGS10 in transcriptionally active regions of the nucleus suggests an unforeseen role of RGS10 in modulating gene expression.

A Culture Device Demonstrates that Hydrostatic Pressure Increases mRNA of RGS5 in Neuroblastoma and CHC1-L in Lymphocytic Cells

Previous studies demonstrated that mechanical forces affect a wide range of cellular behaviors. These forces regulate important cellular responses in the human body and consist of gravity, hydrostatic pressure, stretch, and shear stress, which is exerted on the vascular system by the passage of blood flow. We reasoned that these forces might be significant and dynamic regulators of cellular functions within the human body. While cellular effects of stretch and shear stress have been studied particularly with endothelial cells, little is known about the effects of gravity and hydrostatic pressure to cells. To examine the direct effect of hydrostatic pressure, we developed a culture device to confer hydrostatic pressures to cells ranging from 0 to 1,000 psi. We subjected human neuroblastoma cells and rIL-2-activated lymphocytes to a constant pressure of 20 or 100 psi for 48 h and attempted to identify genes regulated by hydrostatic pressure. Genes of regulator of G-protein signaling 5 in neuroblastoma cells and CHC1-L in lymphocytes increased after exposure to hydrostatic pressure. The results demonstrated that hydrostatic pressure directly regulates the expression of specific genes in mammalian cells. Moreover, there may be some underlying mechanisms that have common effects in altered physical environments. Our in vitro culture system may provide some insight into the mechanisms through the intracellular processes affected by mechanical forces.

Regulation of RGS proteins by chronic morphine in rat locus coeruleus

The present study explored a possible role for RGS (regulators of G protein signalling) proteins in the long term actions of morphine in the locus coeruleus (LC), a brainstem region implicated in opiate physical dependence and withdrawal. Morphine influences LC neurons through activation of micro -opioid receptors, which, being Gi/o-linked, would be expected to be modulated by RGS proteins. We focused on several RGS subtypes that are known to be expressed in this brain region. Levels of mRNAs encoding RGS2, -3, -4, -5, -7, -8 and -11 are unchanged following chronic morphine, but RGS2 and -4 mRNA levels are increased 2-3-fold 6 h following precipitation of opiate withdrawal. The increases in RGS2 and -4 mRNA peak after 6 h of withdrawal and return to control levels by 24 h. Immunoblot analysis of RGS4 revealed a striking divergence between mRNA and protein responses in LC: protein levels are elevated twofold following chronic morphine and decrease to control values by 6 h of withdrawal. In contrast, levels of RGS7 and -11 proteins, the only other subtypes for which antibodies are available, were not altered by these treatments. Intracellular application of wild-type RGS4, but not a GTPase accelerating-deficient mutant of RGS4, into LC neurons diminished electrophysiological responses to morphine. The observed subtype- and time-specific regulation of RGS4 protein and mRNA, and the diminished morphine-induced currents in the presence of elevated RGS4 protein levels, indicate that morphine induction of RGS4 could contribute to aspects of opiate tolerance and dependence displayed by LC neurons.

Striatal gene expression of RGS2 and RGS4 is specifically mediated by dopamine D1 and D2 receptors: clues for RGS2 and RGS4 functions

Of all partners involved in G-protein coupled receptor (GPCR) signalling, the regulator of G-protein signalling (RGS) proteins are the only ones showing fast gene expression changes after various stimuli. These expression changes can offer feedback regulation to GPCR signalling as RGS accelerate the return of G-proteins to their inactive form and exert regulatory functions on intracellular effectors. However, it is not yet known which RGS regulate which receptor transduction pathways in the brain. To start to answer this question, we studied the influence of specific agonists and antagonists of the dopamine D1 and D2 receptors on the gene expression of the five most abundant RGS in the striatum: RGS2, RGS4, RGS8, RGS9 and RGS10. Only changes in RGS2 and RGS4 mRNA levels were observed. The D1 agonist SKF82958 and D2 antagonist haloperidol caused an up-regulation of RGS2 (+ 38.0% and + 41.6%, respectively). The D1 antagonist SCH23390 and D2 agonist quinpirole caused a down-regulation of RGS2 (- 25.0% and - 35.0%) and an up-regulation of RGS4 (+ 57.2% and + 52.5%). D1 and D2 receptors exert opposite effects on RGS2 expression, as they do on cAMP levels, suggesting a cAMP-mediated transcription of RGS2. This was confirmed by the unique induction of RGS2 (+ 111.1%) observed in the periventricular zone of the striatum after intracerebroventricular injection of forskolin. RGS4 was up-regulated only when RGS2 was down-regulated. This suggests that both RGS exert distinct functions. Considering the coupling of D1 and D2 receptors to the intracellular effector adenylate cyclase 5 (AC5) through their respective Galpha subunits in the striatum, our data allow us to suggest that RGS2 regulates the D1/Galphaolf/AC5 pathway and RGS4 the D2/Galphao/AC5 pathway.