RGS2 determines short-term synaptic plasticity in hippocampal neurons by regulating Gi/o-mediated inhibition of presynaptic Ca2+ channels

RGS2 attenuates alveolar macrophage damage by inhibiting the Gq/11-Ca2+ pathway during cowshed PM2.5 exposure, and aberrant RGS2 expression is associated with TLR2/4 activation

Staff and animals in livestock buildings are constantly exposed to fine particulate matter (PM2.5), which affects their respiratory health. However, its exact pathogenic mechanism remains unclear. Regulator of G-protein signaling 2 (RGS2) has been reported to play a regulatory role in pneumonia. The aim of this study was to explore the therapeutic potential of RGS2 in cowshed PM2.5-induced respiratory damage. PM2.5 was collected from a cattle farm, and the alveolar macrophages (NR8383) of the model animal rat were stimulated with different treatment conditions of cowshed PM2.5. The RGS2 overexpression vector was constructed and transfected it into cells. Compared with the control group, cowshed PM2.5 significantly induced a decrease in cell viability and increased the levels of apoptosis and proinflammatory factor expression. Overexpression of RGS2 ameliorated the above-mentioned cellular changes induced by cowshed PM2.5. In addition, PM2.5 has significantly induced intracellular Ca2+ dysregulation. Affinity inhibition of Gq/11 by RGS2 attenuated the cytosolic calcium signaling pathway mediated by PLCβ/IP3R. To further investigate the causes and mechanisms of action of differential RGS2 expression, the possible effects of oxidative stress and TLR2/4 activation were investigated. The results have shown that RGS2 expression was not only regulated by oxidative stress-induced nitric oxide during cowshed PM2.5 cells stimulation but the activation of TLR2/4 had also an important inhibitory effect on its protein expression. The present study demonstrates the intracellular Ca2+ regulatory role of RGS2 during cellular injury, which could be a potential target for the prevention and treatment of PM2.5-induced respiratory injury.

Aggression modulator: Understanding the multifaceted role of the dorsal raphe nucleus

Aggressive behavior is instinctively driven behavior that helps animals to survive and reproduce and is closely related to multiple behavioral and physiological processes. The dorsal raphe nucleus (DRN) is an evolutionarily conserved midbrain structure that regulates aggressive behavior by integrating diverse brain inputs. The DRN consists predominantly of serotonergic (5-HT:5-hydroxytryptamine) neurons and decreased 5-HT activity was classically thought to increase aggression. However, recent studies challenge this 5-HT deficiency model, revealing a more complex role for the DRN 5-HT system in aggression. Furthermore, emerging evidence has shown that non-5-HT populations in the DRN and specific neural circuits contribute to the escalation of aggressive behavior. This review argues that the DRN serves as a multifaceted modulator of aggression, acting not only via 5-HT but also via other neurotransmitters and neural pathways, as well as different subsets of 5-HT neurons. In addition, we discuss the contribution of DRN neurons in the behavioral and physiological aspects implicated in aggressive behavior, such as arousal, reward, and impulsivity, to further our understanding of DRN-mediated aggression modulation.

Dissecting the molecular basis for the modulation of neurotransmitter GPCR signaling by GINIP

It is well established that G-protein-coupled receptors (GPCRs) stimulated by neurotransmitters are critical for neuromodulation. Much less is known about how heterotrimeric G-protein (Gαβγ) regulation after receptor-mediated activation contributes to neuromodulation. Recent evidence indicates that the neuronal protein GINIP shapes GPCR inhibitory neuromodulation via a unique mechanism of G-protein regulation that controls pain and seizure susceptibility. However, the molecular basis of this mechanism remains ill-defined because the structural determinants of GINIP responsible for binding and regulating G proteins are not known. Here, we combined hydrogen-deuterium exchange mass spectrometry, computational structure predictions, biochemistry, and cell-based biophysical assays to demonstrate an effector-like binding mode of GINIP to Gαi. Specific amino acids of GINIP's PHD domain first loop are essential for G-protein binding and subsequent regulation of Gαi-GTP and Gβγ signaling upon neurotransmitter GPCR stimulation. In summary, these findings shed light onto the molecular basis for a post-receptor mechanism of G-protein regulation that fine-tunes inhibitory neuromodulation.

Dissecting the molecular basis for the modulation of neurotransmitter GPCR signaling by GINIP

It is well-established that activation of heterotrimeric G-proteins (Gαβγ) by G-protein-coupled receptors (GPCRs) stimulated by neurotransmitters is a key mechanism underlying neuromodulation. Much less is known about how G-protein regulation after receptor-mediated activation contributes to neuromodulation. Recent evidence indicates that the neuronal protein GINIP shapes GPCR inhibitory neuromodulation via a unique mechanism of G-protein regulation that controls neurological processes like pain and seizure susceptibility. However, the molecular basis of this mechanism remains ill-defined because the structural determinants of GINIP responsible for binding Gαi subunits and regulating G-protein signaling are not known. Here, we combined hydrogen-deuterium exchange mass-spectrometry, protein folding predictions, bioluminescence resonance energy transfer assays, and biochemical experiments to identify the first loop of the PHD domain of GINIP as an obligatory requirement for Gαi binding. Surprisingly, our results support a model in which GINIP undergoes a long-range conformational change to accommodate Gαi binding to this loop. Using cell-based assays, we demonstrate that specific amino acids in the first loop of the PHD domain are essential for the regulation of Gαi-GTP and free Gβγ signaling upon neurotransmitter GPCR stimulation. In summary, these findings shed light onto the molecular basis for a post-receptor mechanism of G-protein regulation that fine-tunes inhibitory neuromodulation.

Reduced Blood RGS2 Expression in Mild Cognitive Impairment Patients

Regulator of G protein signaling 2 (RGS2) is a gene involved in neuronal plasticity and synaptic signaling, whose expression in the brain is altered in neuropsychiatric and neurodegenerative disorders. Microarray data from large datasets suggested reduced RGS2 mRNA levels in the post-mortem brain tissue and blood of Alzheimer’s disease (AD) patients. The results were previously confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) only ex vivo in lymphoblastoid cell lines derived from AD patients and controls. In this study, we compared RGS2 mRNA levels in peripheral blood samples from 69 mild cognitive impairment (MCI) patients to 50 age- and sex-matched non-cognitively impaired controls, out of which 25 patients were monitored at 1 year. We found that RGS2 was indeed downregulated in the peripheral blood of these patients (FR = −1.60, p < 0.001), and despite disease-specific therapy, RGS2 transcript levels continued to decrease at 1 year. The results suggest that RGS2 seems to be involved in AD pathology and progression and can be introduced in a panel of blood AD biomarkers.

Dynamic dichotomy of accumbal population activity underlies cocaine sensitization

Locomotor sensitization (LS) is an early behavioral adaptation to addictive drugs, driven by the increase of dopamine in the Nucleus Accumbens (NAc). However, the effect on accumbal population activity remains elusive. Here, we used single-cell calcium imaging in mice to record the activity of dopamine-1-receptor (D1R) and dopamine-2-receptor (D2R) expressing spiny projection neurons (SPNs) during cocaine LS. Acute exposure to cocaine elevated D1R SPN activity and reduced D2R SPN activity, albeit with high variability between neurons. During LS, the number of D1R and D2R neurons responding in opposite directions increased. Moreover, preventing LS by inhibition of the ERK signaling pathway decreased the number of cocaine responsive D1R SPNs, but had little effect on D2R SPNs. These results indicate that accumbal population dichotomy is dynamic and contains a subgroup of D1R SPNs that eventually drives LS. Insights into the drug-related activity dynamics provides a foundation for understanding the circuit-level addiction pathogenesis.

RGS14 Regulation of Post-Synaptic Signaling and Spine Plasticity in Brain

The regulator of G-protein signaling 14 (RGS14) is a multifunctional signaling protein that regulates post synaptic plasticity in neurons. RGS14 is expressed in the brain regions essential for learning, memory, emotion, and stimulus-induced behaviors, including the basal ganglia, limbic system, and cortex. Behaviorally, RGS14 regulates spatial and object memory, female-specific responses to cued fear conditioning, and environmental- and psychostimulant-induced locomotion. At the cellular level, RGS14 acts as a scaffolding protein that integrates G protein, Ras/ERK, and calcium/calmodulin signaling pathways essential for spine plasticity and cell signaling, allowing RGS14 to naturally suppress long-term potentiation (LTP) and structural plasticity in hippocampal area CA2 pyramidal cells. Recent proteomics findings indicate that RGS14 also engages the actomyosin system in the brain, perhaps to impact spine morphogenesis. Of note, RGS14 is also a nucleocytoplasmic shuttling protein, where its role in the nucleus remains uncertain. Balanced nuclear import/export and dendritic spine localization are likely essential for RGS14 neuronal functions as a regulator of synaptic plasticity. Supporting this idea, human genetic variants disrupting RGS14 localization also disrupt RGS14’s effects on plasticity. This review will focus on the known and unexplored roles of RGS14 in cell signaling, physiology, disease and behavior.

The histone deacetylase inhibitor PCI-24781 impairs calcium influx and inhibits proliferation and metastasis in breast cancer

Histone deacetylases (HDACs) are involved in key cellular processes and have been implicated in cancer. As such, compounds that target HDACs or drugs that target epigenetic markers may be potential candidates for cancer therapy. This study was therefore aimed to identify a potential epidrug with low toxicity and high efficiency as anti-tumor agents. Methods: We first screened an epigenetic small molecule inhibitor library to screen for an epidrug for breast cancer. The candidate was identified as PCI-24781 and was characterized for half maximal inhibitory concentration (IC₅₀), for specificity to breast cancer cells, and for effects on carcinogenesis and metastatic properties of breast cancer cell lines in vitro. A series of in silico and in vitro analyses were further performed of PCI-24781 to identify and understand its target. Results: Screening of an epigenetic inhibitor library in MDA-MB-231 cells, a malignant cancer cell line, showed that PCI-24781 is a potential anti-tumor drug specific to breast cancer. Ca²⁺ related pathways were identified as a potential target of PCI-24781. Further analyses showed that PCI-24781 inhibited Gαq-PLCβ3-mediated calcium signaling by activating the expression of regulator of G-protein signaling 2 (RGS2) to reduce cell proliferation, metastasis, and differentiation, resulting in cell death in breast cancer. In addition, RGS2 depletion reversed anti-tumor effect and inhibition of calcium influx induced by PCI-24781 treatment in breast cancer cells. Conclusions: We have demonstrated that PCI-24781 is an effective anti-tumor therapeutic agent that targets calcium signaling by activating RGS2. This study also provides a novel perspective into the use of HDAC inhibitors for cancer therapy.

RGS2 drives male aggression in mice via the serotonergic system

Aggressive behavior in our modern, civilized society is often counterproductive and destructive. Identifying specific proteins involved in the disease can serve as therapeutic targets for treating aggression. Here, we found that overexpression of RGS2 in explicitly serotonergic neurons augments male aggression in control mice and rescues male aggression in Rgs2-/- mice, while anxiety is not affected. The aggressive behavior is directly correlated to the immediate early gene c-fos induction in the dorsal raphe nuclei and ventrolateral part of the ventromedial nucleus hypothalamus, to an increase in spontaneous firing in serotonergic neurons and to a reduction in the modulatory action of Gi/o and Gq/11 coupled 5HT and adrenergic receptors in serotonergic neurons of Rgs2-expressing mice. Collectively, these findings specifically identify that RGS2 expression in serotonergic neurons is sufficient to drive male aggression in mice and as a potential therapeutic target for treating aggression.

Presynaptic Calcium Channels

Presynaptic Ca²⁺ entry occurs through voltage-gated Ca²⁺ (Ca_V) channels which are activated by membrane depolarization. Depolarization accompanies neuronal firing and elevation of Ca²⁺ triggers neurotransmitter release from synaptic vesicles. For synchronization of efficient neurotransmitter release, synaptic vesicles are targeted by presynaptic Ca²⁺ channels forming a large signaling complex in the active zone. The presynaptic Ca_V2 channel gene family (comprising Ca_V2.1, Ca_V2.2, and Ca_V2.3 isoforms) encode the pore-forming α1 subunit. The cytoplasmic regions are responsible for channel modulation by interacting with regulatory proteins. This article overviews modulation of the activity of Ca_V2.1 and Ca_V2.2 channels in the control of synaptic strength and presynaptic plasticity.

Retinoid receptor-based signaling plays a role in voltage-dependent inhibition of invertebrate voltage-gated Ca2+ channels

The retinoic acid receptor (RAR) and retinoid X receptor (RXR) mediate the cellular effects of retinoids (derivatives of vitamin A). Both RAR and RXR signaling events are implicated in hippocampal synaptic plasticity. Furthermore, retinoids can interact with calcium signaling during homeostatic plasticity. We recently provided evidence that retinoids attenuate calcium current (I _Ca) through neuronal voltage-gated calcium channels (VGCCs). We now examined the possibility that constitutive activity of neuronal RXR and/or RAR alters calcium influx via the VGCCs. We found that in neurons of the mollusk Lymnaea stagnalis, two different RXR antagonists (PA452 and HX531) had independent and opposing effects on I _Ca that were also time-dependent; whereas the RXR pan-antagonist PA452 enhanced I _Ca, HX531 reduced I _Ca Interestingly, this effect of HX531 occurred through voltage-dependent inhibition of VGCCs, a phenomenon known to influence neurotransmitter release from neurons. This inhibition appeared to be independent of G proteins and was largely restricted to Ca_v2 Ca²⁺ channels. Of note, an RAR pan-antagonist, LE540, also inhibited I _Ca but produced G protein-dependent, voltage-dependent inhibition of VGCCs. These findings provide evidence that retinoid receptors interact with G proteins in neurons and suggest mechanisms by which retinoids might affect synaptic calcium signaling.

3D-QSARs and molecular dynamics simulation studies on induced fit binding of flavones to human aldose reductase

Communicated by Ramaswamy H. Sarma.

The Role of G-proteins and G-protein Regulating Proteins in Depressive Disorders

Progress toward new antidepressant therapies has been relatively slow over the past few decades, with the result that individuals suffering from depression often struggle to find an effective treatment – a process often requiring months. Furthermore, the neural factors that contribute to depression remain poorly understood, and there are many open questions regarding the mechanism of action of existing antidepressants. A better understanding of the molecular processes that underlie depression and contribute to antidepressant efficacy is therefore badly needed. In this review we highlight research investigating the role of G-proteins and the regulators of G-protein signaling (RGS) proteins, two protein families that are intimately involved in both the genesis of depressive states and the action of antidepressant drugs. Many antidepressants are known to indirectly affect the function of these proteins. Conversely, dysfunction of the G-protein and RGS systems can affect antidepressant efficacy. However, a great deal remains unknown about how these proteins interact with antidepressants. Findings pertinent to each individual G-protein and RGS protein are summarized from in vitro, in vivo, and clinical studies.

Inhibitory Signaling to Ion Channels in Hippocampal Neurons Is Differentially Regulated by Alternative Macromolecular Complexes of RGS7

The neuromodulatory effects of GABA on pyramidal neurons are mediated by GABA_B receptors (GABA_BRs) that signal via a conserved G-protein-coupled pathway. Two prominent effectors regulated by GABA_BRs include G-protein inwardly rectifying K⁺ (GIRK) and P/Q/N type voltage-gated Ca²⁺ (Ca_V2) ion channels that control excitability and synaptic output of these neurons, respectively. Regulator of G-protein signaling 7 (RGS7) has been shown to control GABA_B effects, yet the specificity of its impacts on effector channels and underlying molecular mechanisms is poorly understood. In this study, we show that hippocampal RGS7 forms two distinct complexes with alternative subunit configuration bound to either membrane protein R7BP (RGS7 binding protein) or orphan receptor GPR158. Quantitative biochemical experiments show that both complexes account for targeting nearly the entire pool of RGS7 to the plasma membrane. We analyzed the effect of genetic elimination in mice of both sexes and overexpression of various components of RGS7 complex by patch-clamp electrophysiology in cultured neurons and brain slices. We report that RGS7 prominently regulates GABA_BR signaling to Ca_V2, in addition to its known involvement in modulating GIRK. Strikingly, only complexes containing R7BP, but not GPR158, accelerated the kinetics of both GIRK and Ca_V2 modulation by GABA_BRs. In contrast, GPR158 overexpression exerted the opposite effect and inhibited RGS7-assisted temporal modulation of GIRK and Ca_V2 by GABA. Collectively, our data reveal mechanisms by which distinctly composed macromolecular complexes modulate the activity of key ion channels that mediate the inhibitory effects of GABA on hippocampal CA1 pyramidal neurons.SIGNIFICANCE STATEMENT This study identifies the contributions of distinct macromolecular complexes containing a major G-protein regulator to controlling key ion channel function in hippocampal neurons with implications for understanding molecular mechanisms underlying synaptic plasticity, learning, and memory.

Regulator of G protein signaling 2 differentially regulates nicotine-induced anxiolytic- and antidepressant-like effects in mice

This study assessed the role of regulator of G protein signaling 2 (RGS2) in nicotine-induced anxiolytic- and antidepressant-like effects using RGS2 wildtype (WT) and RGS2 knockout (KO) mice. RGS2 negatively regulates monoaminergic neurotransmission, which is implicated in the pathology of anxiety and depression. We hypothesized that deletion of RGS2 would enhance nicotine-induced anxiolytic- and antidepressant-like effects, which were assessed using the elevated plus maze and tail suspension tests, respectively. Anxiolytic-like effects were observed in both RGS2 WT and KO mice after administration of low dose of nicotine (0.05 mg/kg, base) compared to respective saline controls. Additionally, administration of nicotine (0.1 mg/kg, base) compared to saline resulted in anxiolytic-like effects in RGS2 KO mice, but not RGS2 WT mice, suggesting genetic deletion of RGS2 facilitated anxiolytic-like effects of nicotine. Administration of nicotine (0.5 and 1 mg/kg, base) compared to saline resulted in antidepressant-like effects in RGS2 WT mice. Antidepressant-like effects were observed in RGS2 KO mice only at the highest tested dose of nicotine (1 mg/kg, base) compared to saline controls, suggesting that genetic deletion of RGS2 decreased sensitivity to antidepressant-like effects of nicotine. Together, the data suggest that RGS2 differentially regulated nicotine-induced affective behavioral responses. These data suggest that individuals with RGS2 polymorphisms may experience differential affective responses to tobacco smoking, which may make them vulnerable to developing nicotine addiction.

Interplay between negative and positive design elements in Gα helical domains of G proteins determines interaction specificity toward RGS2

Regulators of G protein signaling (RGS) proteins inactivate Gα subunits, thereby controlling G protein-coupled signaling networks. Among all RGS proteins, RGS2 is unique in interacting only with the Gα_q but not with the Gα_i subfamily. Previous studies suggested that this specificity is determined by the RGS domain and, in particular, by three RGS2-specific residues that lead to a unique mode of interaction with Gα_q This interaction was further proposed to act through contacts with the Gα GTPase domain. Here, we combined energy calculations and GTPase activity measurements to determine which Gα residues dictate specificity toward RGS2. We identified putative specificity-determining residues in the Gα helical domain, which among G proteins is found only in Gα subunits. Replacing these helical domain residues in Gα_i with their Gα_q counterparts resulted in a dramatic specificity switch toward RGS2. We further show that Gα-RGS2 specificity is set by Gα_i residues that perturb interactions with RGS2, and by Gα_q residues that enhance these interactions. These results show, for the first time, that the Gα helical domain is central to dictating specificity toward RGS2, suggesting that this domain plays a general role in governing Gα-RGS specificity. Our insights provide new options for manipulating RGS-G protein interactions in vivo, for better understanding of their 'wiring' into signaling networks, and for devising novel drugs targeting such interactions.

Visual tuning in the flashlight fish Anomalops katoptron to detect blue, bioluminescent light

Bioluminescence is a fascinating phenomenon and can be found in many different organisms including fish. It has been suggested that bioluminescence is used for example for defense, prey attraction, and for intraspecific communication to attract for example sexual partners. The flashlight fish, Anomalops katoptron (A. katoptron), is a nocturnal fish that produces bioluminescence and lives in shallow waters, which makes it ideal for laboratory studies. In order to understand A. katoptron's ability to detect bioluminescent light (480 to 490 nm) at night, we characterized the visual system adaptation of A. katoptron using phylogenetic, electrophysiological and behavioral studies. We found that the retinae of A. katoptron contain rods and sparse cones. A. katoptron retinae express two main visual pigments, rhodopsin (RH1), and to a lesser extent, rhodopsin-like opsin (RH2). Interestingly, recombinant RH1 and RH2 are maximally sensitive to a wavelength of approximately 490 nm light (λmax), which correspond to the spectral peak of in vivo electroretinogram (ERG) measurements. In addition, behavioral assays revealed that A. katoptron is attracted by low intensity blue but not red light. Collectively, our results suggest that the A. katoptron visual system is optimized to detect blue light in the frequency range of its own bioluminescence and residual starlight.

Regulator of G protein signaling 14 (RGS14) is expressed pre- and postsynaptically in neurons of hippocampus, basal ganglia, and amygdala of monkey and human brain

Regulator of G protein signaling 14 (RGS14) is a multifunctional signaling protein primarily expressed in mouse pyramidal neurons of hippocampal area CA2 where it regulates synaptic plasticity important for learning and memory. However, very little is known about RGS14 protein expression in the primate brain. Here, we validate the specificity of a new polyclonal RGS14 antibody that recognizes not only full-length RGS14 protein in primate, but also lower molecular weight forms of RGS14 protein matching previously predicted human splice variants. These putative RGS14 variants along with full-length RGS14 are expressed in the primate striatum. By contrast, only full-length RGS14 is expressed in hippocampus, and shorter variants are completely absent in rodent brain. We report that RGS14 protein immunoreactivity is found both pre- and postsynaptically in multiple neuron populations throughout hippocampal area CA1 and CA2, caudate nucleus, putamen, globus pallidus, substantia nigra, and amygdala in adult rhesus monkeys. A similar cellular expression pattern of RGS14 in the monkey striatum and hippocampus was further confirmed in humans. Our electron microscopy data show for the first time that RGS14 immunostaining localizes within nuclei of striatal neurons in monkeys. Taken together, these findings suggest new pre- and postsynaptic regulatory functions of RGS14 and RGS14 variants, specific to the primate brain, and provide evidence for unconventional roles of RGS14 in the nuclei of striatal neurons potentially important for human neurophysiology and disease.

Chronic intermittent ethanol exposure selectively alters the expression of Gα subunit isoforms and RGS subtypes in rat prefrontal cortex

Chronic alcohol exposure induces pronounced changes in GPCR-mediated G-protein signaling. Recent microarray and RNA-seq analyses suggest associations between alcohol abuse and the expression of genes involved in G-protein signaling. The activity of G-proteins (e.g. Gαi/o and Gαq) is negatively modulated by regulator of G-protein signaling (RGS) proteins which are implicated in drugs of abuse including alcohol. The present study used 7days of chronic intermittent ethanol exposure followed by 24h withdrawal (CIE) to investigate changes in mRNA and protein levels of G-protein subunit isoforms and RGS protein subtypes in rat prefrontal cortex, a region associated with cognitive deficit attributed to excessive alcohol drinking. We found that this ethanol paradigm induced differential expression of Gα subunits and RGS subtypes. For example, there were increased mRNA and protein levels of Gαi1/3 subunits and no changes in the expression of Gαs and Gαq subunits in ethanol-treated animals. Moreover, CIE increased the mRNA but not the protein levels of Gαo. Additionally, a modest increase in Gαi2 mRNA level by CIE was accompanied by a pronounced increase in its protein level. Interestingly, we found that CIE increased mRNA and protein levels of RGS2, RGS4, RGS7 and RGS19 but had no effect on the expression of RGS5, RGS6, RGS8, RGS12 or RGS17. Changes in the expression of Gα subunits and RGS subtypes could contribute to the functional alterations of certain GPCRs following chronic ethanol exposure. The present study suggests that RGS proteins may be potential new targets for intervention of alcohol abuse via modification of Gα-mediated GPCR function.

Knockdown of regulator of G-protein signalling 2 (Rgs2) leads to abnormal early mouse embryo development in vitro

Regulator of G-protein signalling 2 (Rgs2) is involved in G-protein-mediated signalling by negatively regulating the activity of the G-protein α-subunit. In the present study, the expression patterns of Rgs2 in mouse ovarian tissues and early embryos were determined by semiquantitative reverse transcription-polymerase chain reaction, immunohistochemistry and immunofluorescent analyses. Rgs2 expression was observed in the ovarian tissues of adult female mice, with an almost equal expression levels during different stages of the oestrous cycle. Rgs2 was abundant in the cytoplasm, membrane, nuclei and spindles of intact polar bodies in mouse early embryos at different developmental stages from the zygote to blastocyst. The effect of Rgs2 knockdown on early embryonic development in vitro was examined by microinjecting Rgs2-specific short interfering (si) RNAs into mouse zygotes. Knockdown of endogenous Rgs2 expression led to abnormal embryonic development in vitro, with a considerable number of early embryos arrested at the 2- or 4-cell stage. Moreover, mRNA expression of three zygotic gene activation-related genes (i.e. Zscan4, Tcstv1 and MuERV-L) was decreased significantly in 2-cell arrested embryos. These results suggest that Rgs2 plays a critical role in early embryo development.

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 modulates the activity and internalization of dopamine D2 receptors in neuroblastoma N2A cells

Dysregulated expression and function of dopamine D2 receptors (D2Rs) are implicated in drug addiction, Parkinson's disease and schizophrenia. In the current study, we examined whether D2Rs are modulated by regulator of G protein signaling 2 (RGS2), a member of the RGS family that regulates G protein signaling via acceleration of GTPase activity. Using neuroblastoma 2a (N2A) cells, we found that RGS2 was immunoprecipitated by aluminum fluoride-activated Gαi2 proteins. RGS2 siRNA knockdown enhanced membrane [(35)S] GTPγS binding to activated Gαi/o proteins, augmented inhibition of cAMP accumulation and increased ERK phosphorylation in the presence of a D2/D3R agonist quinpirole when compared to scrambled siRNA treatment. These data suggest that RGS2 is a negative modulator of D2R-mediated Gαi/o signaling. Moreover, RGS2 knockdown slightly increased constitutive D2R internalization and markedly abolished quinpirole-induced D2R internalization assessed by immunocytochemistry. RGS2 knockdown did not compromise agonist-induced β-arrestin membrane recruitment; however, it prevents β-arrestin dissociation from the membrane after prolonged quinpirole treatment during which time β-arrestin moved away from the membrane in control cells. Additionally, confocal microscopy analysis of β-arrestin post-endocytic fate revealed that quinpirole treatment caused β-arrestin to translocate to the early and the recycling endosome in a time-dependent manner in control cells whereas translocation of β-arrestin to these endosomes did not occur in RGS2 knockdown cells. The impaired β-arrestin translocation likely contributed to the abolishment of quinpirole-stimulated D2R internalization in RGS2 knockdown cells. Thus, RGS2 is integral for β-arrestin-mediated D2R internalization. The current study revealed a novel regulation of D2R signaling and internalization by RGS2 proteins.

Roles for Regulator of G Protein Signaling Proteins in Synaptic Signaling and Plasticity

The regulator of G protein signaling (RGS) family of proteins serves critical roles in G protein-coupled receptor (GPCR) and heterotrimeric G protein signal transduction. RGS proteins are best understood as negative regulators of GPCR/G protein signaling. They achieve this by acting as GTPase activating proteins (GAPs) for Gα subunits and accelerating the turnoff of G protein signaling. Many RGS proteins also bind additional signaling partners that either regulate their functions or enable them to regulate other important signaling events. At neuronal synapses, GPCRs, G proteins, and RGS proteins work in coordination to regulate key aspects of neurotransmitter release, synaptic transmission, and synaptic plasticity, which are necessary for central nervous system physiology and behavior. Accumulating evidence has revealed key roles for specific RGS proteins in multiple signaling pathways at neuronal synapses, regulating both pre- and postsynaptic signaling events and synaptic plasticity. Here, we review and highlight the current knowledge of specific RGS proteins (RGS2, RGS4, RGS7, RGS9-2, and RGS14) that have been clearly demonstrated to serve critical roles in modulating synaptic signaling and plasticity throughout the brain, and we consider their potential as future therapeutic targets.

Spinocerebellar ataxia type 6 protein aggregates cause deficits in motor learning and cerebellar plasticity

Spinocerebellar ataxia type 6 (SCA6) is linked to poly-glutamine (polyQ) within the C terminus (CT) of the pore-forming subunits of P/Q-type Ca(2+) channels (Cav2.1) and is characterized by CT protein aggregates found in cerebellar Purkinje cells (PCs). One hypothesis regarding SCA6 disease is that a CT fragment of the Cav2.1 channel, which is detected specifically in cytosolic and nuclear fractions in SCA6 patients, is associated with the SCA6 pathogenesis. To test this hypothesis, we expressed P/Q-type channel protein fragments from two different human CT splice variants, as predicted from SCA6 patients, in PCs of mice using viral and transgenic approaches. These splice variants represent a short (CT-short without polyQs) and a long (CT-long with 27 polyQs) CT fragment. Our results show that the different splice variants of the CTs differentially distribute within PCs, i.e., the short CTs reveal predominantly nuclear inclusions, whereas the long CTs prominently reveal both nuclear and cytoplasmic aggregates. Postnatal expression of CTs in PCs in mice reveals that only CT-long causes SCA6-like symptoms, i.e., deficits in eyeblink conditioning (EBC), ataxia, and PC degeneration. The physiological phenotypes associated specifically with the long CT fragment can be explained by an impairment of LTD and LTP at the parallel fiber-to-PC synapse and alteration in spontaneous PC activity. Thus, our results suggest that the polyQ carrying the CT fragment of the P/Q-type channel is sufficient to cause SCA6 pathogenesis in mice and identifies EBC as a new diagnostic strategy to evaluate Ca(2+) channel-mediated human diseases.

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.

Regulation of Gβγi-dependent PLC-β3 activity in smooth muscle: inhibitory phosphorylation of PLC-β3 by PKA and PKG and stimulatory phosphorylation of Gαi-GTPase-activating protein RGS2 by PKG

In gastrointestinal smooth muscle, agonists that bind to Gi-coupled receptors activate preferentially PLC-β3 via Gβγ to stimulate phosphoinositide (PI) hydrolysis and generate inositol 1,4,5-trisphosphate (IP3) leading to IP3-dependent Ca(2+) release and muscle contraction. In the present study, we identified the mechanism of inhibition of PLC-β3-dependent PI hydrolysis by cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG). Cyclopentyl adenosine (CPA), an adenosine A1 receptor agonist, caused an increase in PI hydrolysis in a concentration-dependent fashion; stimulation was blocked by expression of the carboxyl-terminal sequence of GRK2(495-689), a Gβγ-scavenging peptide, or Gαi minigene but not Gαq minigene. Isoproterenol and S-nitrosoglutathione (GSNO) induced phosphorylation of PLC-β3 and inhibited CPA-induced PI hydrolysis, Ca(2+) release, and muscle contraction. The effect of isoproterenol on all three responses was inhibited by PKA inhibitor, myristoylated PKI, or AKAP inhibitor, Ht-31, whereas the effect of GSNO was selectively inhibited by PKG inhibitor, Rp-cGMPS. GSNO, but not isoproterenol, also phosphorylated Gαi-GTPase-activating protein, RGS2, and enhanced association of Gαi3-GTP and RGS2. The effect of GSNO on PI hydrolysis was partly reversed in cells (i) expressing constitutively active GTPase-resistant Gαi mutant (Q204L), (ii) phosphorylation-site-deficient RGS2 mutant (S46A/S64A), or (iii) siRNA for RGS2. We conclude that PKA and PKG inhibit Gβγi-dependent PLC-β3 activity by direct phosphorylation of PLC-β3. PKG, but not PKA, also inhibits PI hydrolysis indirectly by a mechanism involving phosphorylation of RGS2 and its association with Gαi-GTP. This allows RGS2 to accelerate Gαi-GTPase activity, enhance Gαβγi trimer formation, and inhibit Gβγi-dependent PLC-β3 activity.

MicroRNA hsa-miR-4717-5p regulates RGS2 and may be a risk factor for anxiety-related traits

Regulator of G-protein Signaling 2 (RGS2) is a key regulator of G-protein-coupled signaling pathways involved in fear and anxiety. Data from rodent models and genetic analysis of anxiety-related traits and disorders in humans suggest down-regulation of RGS2 expression to be a risk factor for anxiety. Here we investigated, whether genetic variation in microRNAs mediating posttranscriptional down-regulation of RGS2 may be a risk factor for anxiety as well. 75 microRNAs predicted to regulate RGS2 were identified by four bioinformatic algorithms and validated experimentally by luciferase reporter gene assays. Specificity was confirmed for six microRNAs (hsa-miR-1271-5p, hsa-miR-22-3p, hsa-miR-3591-3p, hsa-miR-377-3p, hsa-miR-4717-5p, hsa-miR-96-5p) by disrupting their seed sequence at the 3' untranslated region of RGS2. Hsa-miR-4717-5p showed the most robust effect on RGS2 and regulated two other candidate genes of anxiety disorders (CNR1 and IKBKE) as well. Two SNPs (rs150925, rs161427) within and 1,000 bp upstream of the hostgene of hsa-miR-4717-5p (MIR4717) show a minor allele frequency greater than 0.05. Both were in high linkage disequilibrium (r(2) = 1, D' = 1) and both major (G) alleles showed a trend for association with panic disorder with comorbid agoraphobia in one of two patient/control samples (combined n(patients) = 497). Dimensional anxiety traits, as described by Anxiety Sensitivity Index (ASI) and Agoraphobic Cognitions Questionnaire (ACQ) were significantly higher among carriers of both major (G) alleles in a combined patient/control sample (n(combined) = 831). Taken together, data indicate that MIR4717 regulates human RGS2 and contributes to the genetic risk towards anxiety-related traits.

Synaptic plasticity, neural circuits, and the emerging role of altered short-term information processing in schizophrenia

Synaptic plasticity alters the strength of information flow between presynaptic and postsynaptic neurons and thus modifies the likelihood that action potentials in a presynaptic neuron will lead to an action potential in a postsynaptic neuron. As such, synaptic plasticity and pathological changes in synaptic plasticity impact the synaptic computation which controls the information flow through the neural microcircuits responsible for the complex information processing necessary to drive adaptive behaviors. As current theories of neuropsychiatric disease suggest that distinct dysfunctions in neural circuit performance may critically underlie the unique symptoms of these diseases, pathological alterations in synaptic plasticity mechanisms may be fundamental to the disease process. Here we consider mechanisms of both short-term and long-term plasticity of synaptic transmission and their possible roles in information processing by neural microcircuits in both health and disease. As paradigms of neuropsychiatric diseases with strongly implicated risk genes, we discuss the findings in schizophrenia and autism and consider the alterations in synaptic plasticity and network function observed in both human studies and genetic mouse models of these diseases. Together these studies have begun to point toward a likely dominant role of short-term synaptic plasticity alterations in schizophrenia while dysfunction in autism spectrum disorders (ASDs) may be due to a combination of both short-term and long-term synaptic plasticity alterations.

RGS2 and RGS4 proteins: New modulators of the κ-opioid receptor signaling

Previous studies have shown that RGS4 associates with the C-termini of μ- and δ-opioid receptors in living cells and plays a key role in Gi/Go protein coupling selectivity and signalling of these receptors [12,20]. To deduce whether similar effects also occur for the κ-opioid receptor (κ-ΟR) and define the ability of members of the Regulators of G protein Signaling (RGS) of the B/R4 subfamily to interact with κ-ΟR subdomains we generated glutathione S-transferase fusion peptides encompassing the carboxyl-termini of κ-OR (κ-CT). Results from pull down experiments indicated that RGS2 and RGS4 directly interact within different domains of the κ-CT. Co-precipitation studies in living cells indicated that RGS2 and RGS4 associate with κ-ΟR constitutively and upon receptor activation and confer selectivity for coupling with a specific subset of G proteins. Expression of both members, RGS2 and/or RGS4, in 293F cells attenuated κ-agonist mediated-adenylyl cyclase inhibition and extracellular signal regulated kinase (ERK1,2) phosphorylation with a different amplitude in their modulatory effect in κ-ΟR signaling. Our findings demonstrate that RGS2 and RGS4 are new interacting partners that play key roles in G protein coupling to negatively regulate κ-ΟR signaling.

Melanocortin 4 receptor activation inhibits presynaptic N-type calcium channels in amygdaloid complex neurons

The melanocortin 4 receptor (MC4R) is a G protein-coupled receptor involved in food intake and energy expenditure regulation. MC4R activation modifies neuronal activity but the molecular mechanisms by which this regulation occurs remain unclear. Here, we tested the hypothesis that MC4R activation regulates the activity of voltage-gated calcium channels and, as a consequence, synaptic activity. We also tested whether the proposed effect occurs in the amygdala, a brain area known to mediate the anorexigenic actions of MC4R signaling. Using the patch-clamp technique, we found that the activation of MC4R with its agonist melanotan II specifically inhibited 34.5 ± 1.5% of N-type calcium currents in transiently transfected HEK293 cells. This inhibition was concentration-dependent, voltage-independent and occluded by the Gαs pathway inhibitor cholera toxin. Moreover, we found that melanotan II specifically inhibited 25.9 ± 2.0% of native N-type calcium currents and 55.4 ± 14.4% of evoked inhibitory postsynaptic currents in mouse cultured amygdala neurons. In vivo, we found that the MC4R agonist RO27-3225 increased the marker of cellular activity c-Fos in several components of the amygdala, whereas the N-type channel blocker ω conotoxin GVIA increased c-Fos expression exclusively in the central subdivision of the amygdala. Thus, MC4R specifically inhibited the presynaptic N-type channel subtype, and this inhibition may be important for the effects of melanocortin in the central subdivision of the amygdala.

Vitamin B6 reduces hippocampal apoptosis in experimental pneumococcal meningitis

BACKGROUND

Bacterial meningitis caused by Streptococcus pneumoniae leads to death in up to 30% of patients and leaves up to half of the survivors with neurological sequelae. The inflammatory host reaction initiates the induction of the kynurenine pathway and contributes to hippocampal apoptosis, a form of brain damage that is associated with learning and memory deficits in experimental paradigms. Vitamin B6 is an enzymatic cofactor in the kynurenine pathway and may thus limit the accumulation of neurotoxic metabolites and preserve the cellular energy status. The aim of this study in a pneumococcal meningitis model was to investigate the effect of vitamin B6 on hippocampal apoptosis by histomorphology, by transcriptomics and by measurement of cellular nicotine amide adenine dinucleotide content.

METHODS AND RESULTS

Eleven day old Wistar rats were infected with 1x10(6) cfu/ml of S. pneumoniae and randomized for treatment with vitamin B6 or saline as controls. Vitamin B6 led to a significant (p > 0.02) reduction of hippocampal apoptosis. According to functional annotation based clustering, vitamin B6 led to down-regulation of genes involved in processes of inflammatory response, while genes encoding for processes related to circadian rhythm, neuronal signaling and apoptotic cell death were mostly up-regulated.

CONCLUSIONS

Our results provide evidence that attenuation of apoptosis by vitamin B6 is multi-factorial including down-modulation of inflammation, up-regulation of the neuroprotective brain-derived neurotrophic factor and prevention of the exhaustion of cellular energy stores. The neuroprotective effect identifies vitamin B6 as a potential target for the development of strategies to attenuate brain injury in bacterial meningitis.

Early phase of plasticity-related gene regulation and SRF dependent transcription in the hippocampus

Hippocampal organotypic cultures are a highly reliable in vitro model for studying neuroplasticity: in this paper, we analyze the early phase of the transcriptional response induced by a 20 µM gabazine treatment (GabT), a GABA-Ar antagonist, by using Affymetrix oligonucleotide microarray, RT-PCR based time-course and chromatin-immuno-precipitation. The transcriptome profiling revealed that the pool of genes up-regulated by GabT, besides being strongly related to the regulation of growth and synaptic transmission, is also endowed with neuro-protective and pro-survival properties. By using RT-PCR, we quantified a time-course of the transient expression for 33 of the highest up-regulated genes, with an average sampling rate of 10 minutes and covering the time interval [10∶90] minutes. The cluster analysis of the time-course disclosed the existence of three different dynamical patterns, one of which proved, in a statistical analysis based on results from previous works, to be significantly related with SRF-dependent regulation (p-value<0.05). The chromatin immunoprecipitation (chip) assay confirmed the rich presence of working CArG boxes in the genes belonging to the latter dynamical pattern and therefore validated the statistical analysis. Furthermore, an in silico analysis of the promoters revealed the presence of additional conserved CArG boxes upstream of the genes Nr4a1 and Rgs2. The chip assay confirmed a significant SRF signal in the Nr4a1 CArG box but not in the Rgs2 CArG box.

PIP₂ hydrolysis is responsible for voltage independent inhibition of CaV2.2 channels in sympathetic neurons

GPCRs regulate Ca(V)2.2 channels through both voltage dependent and independent inhibition pathways. The aim of the present work was to assess the phosphatidylinositol-4,5-bisphosphate (PIP2) as the molecule underlying the voltage independent inhibition of Ca(V)2.2 channels in SCG neurons. We used a double pulse protocol to study the voltage independent inhibition and changed the PIP(2) concentration by means of blocking the enzyme PLC, filling the cell with a PIP(2) analogue and preventing the PIP(2) resynthesis with wortmannin. We found that voltage independent inhibition requires the activation of PLC and can be hampered by internal dialysis of exogenous PIP(2). In addition, the recovery from voltage independent inhibition is blocked by inhibition of the enzymes involved in the resynthesis of PIP(2). These results support that the hydrolysis of PIP(2) is responsible for the voltage independent inhibition of Ca(V)2.2 channels.

The vasculome of the mouse brain

The blood vessel is no longer viewed as passive plumbing for the brain. Increasingly, experimental and clinical findings suggest that cerebral endothelium may possess endocrine and paracrine properties – actively releasing signals into and receiving signals from the neuronal parenchyma. Hence, metabolically perturbed microvessels may contribute to central nervous system (CNS) injury and disease. Furthermore, cerebral endothelium can serve as sensors and integrators of CNS dysfunction, releasing measurable biomarkers into the circulating bloodstream. Here, we define and analyze the concept of a brain vasculome, i.e. a database of gene expression patterns in cerebral endothelium that can be linked to other databases and systems of CNS mediators and markers. Endothelial cells were purified from mouse brain, heart and kidney glomeruli. Total RNA were extracted and profiled on Affymetrix mouse 430 2.0 micro-arrays. Gene expression analysis confirmed that these brain, heart and glomerular preparations were not contaminated by brain cells (astrocytes, oligodendrocytes, or neurons), cardiomyocytes or kidney tubular cells respectively. Comparison of the vasculome between brain, heart and kidney glomeruli showed that endothelial gene expression patterns were highly organ-dependent. Analysis of the brain vasculome demonstrated that many functionally active networks were present, including cell adhesion, transporter activity, plasma membrane, leukocyte transmigration, Wnt signaling pathways and angiogenesis. Analysis of representative genome-wide-association-studies showed that genes linked with Alzheimer’s disease, Parkinson’s disease and stroke were detected in the brain vasculome. Finally, comparison of our mouse brain vasculome with representative plasma protein databases demonstrated significant overlap, suggesting that the vasculome may be an important source of circulating signals in blood. Perturbations in cerebral endothelial function may profoundly affect CNS homeostasis. Mapping and dissecting the vasculome of the brain in health and disease may provide a novel database for investigating disease mechanisms, assessing therapeutic targets and exploring new biomarkers for the CNS.

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.

Relationship between Rgs2 gene expression level and anxiety and depression-like behaviour in a mutant mouse model: serotonergic involvement

RGS2 is a member of a family of proteins that negatively modulate G-protein coupled receptor transmission. Variations in the RGS2 gene were found to be associated in humans with anxious and depressive phenotypes. We sought to study the relationship of Rgs2 expression level to depression and anxiety-like behavioural features, sociability and brain 5-HT1A and 5-HT1B receptor expression. We studied male mice carrying a mutation that causes lower Rgs2 gene expression, employing mice heterozygous (Het) or homozygous (Hom) for this mutation, or wild-type (WT). Mice were subjected to behavioural tests reflecting depressive-like behaviour [forced swim test (FST), novelty suppressed feeding test (NSFT)], elevated plus maze (EPM) for evaluation of anxiety levels and the three-chamber sociability test. The possible involvement of raphe nucleus 5-HT1A receptors in these behavioural features was examined by 8-OH-DPAT-induced hypothermia. Expression levels of 5-HT1A and 5-HT1B receptors in the cortex, raphe nucleus and hypothalamus were compared among mice of the different Rgs2 genotype groups. NSFT results demonstrated that Hom mice showed more depressive-like features than Rgs2 Het and WT mice. A trend for such a relationship was also suggested by the FST results. EPM and sociability test results showed Hom and Het mice to be more anxious and less sociable than WT mice. In addition Hom and Het mice were characterized by lower basal body temperature and demonstrated less 8-OH-DPAT-induced hypothermia than WT mice. Finally, Hom and Het mice had significantly lower 5-HT1A and 5-HT1B receptor expression levels in the raphe than WT mice. Our findings demonstrate a relationship between Rgs2 gene expression level and a propensity for anxious and depressive-like behaviour and reduced social interaction that may involve changes in serotonergic receptor expression.

Alteration in RGS2 expression level is associated with changes in haloperidol induced extrapyramidal features in a mutant mouse model

Antipsychotic induced Parkinsonism (AIP) is a common adverse effect of antipsychotic drug treatment among schizophrenia patients. Two previous studies showed association of the rs4606 SNP in the 3' untranslated region of the regulator of G protein signaling 2 gene (RGS2) with susceptibility to AIP. Since rs4606 reportedly influences expression of RGS2, we applied a translational approach and studied the effect of chronic (24 days) exposure to haloperidol on AIP-like features in mice carrying a mutation that causes lower Rgs2 gene expression. Haloperidol and vehicle treated male mice heterozygous (HET) or homozygous (HOM) for the mutation, or wild type (WT), were evaluated for open field locomotion, catalepsy duration, pole test performance and rota-rod latency to fall. We showed that in haloperidol treated mice lower Rgs2 expression is associated with better performance on the open field, catalepsy and rota-rod tests but not the pole test. Results were most consistent for the 0.2 mg/kg/d haloperidol dose. These observations support the possible involvement of RGS2 in mechanisms underlying susceptibility to AIP.

Gβ5-RGS complexes are gatekeepers of hyperactivity involved in control of multiple neurotransmitter systems

RATIONALE AND OBJECTIVES

Our knowledge about genes involved in the control of basal motor activity that may contribute to the pathology of the hyperactivity disorders, e.g., attention deficit hyperactivity disorder (ADHD), is limited. Disruption of monoamine neurotransmitter signaling through G protein-coupled receptors (GPCR) is considered to be a major contributing factor to the etiology of the ADHD. Genetic association evidence and functional data suggest that regulators of G protein signaling proteins of the R7 family (R7 RGS) that form obligatory complexes with type 5 G protein beta subunit (Gβ5) and negatively regulate signaling downstream from monoamine GPCRs may play a role in controlling hyperactivity.

METHODS

To test this hypothesis, we conducted behavioral, pharmacological, and neurochemical studies using a genetic mouse model that lacked Gβ5, a subunit essential for the expression of the entire R7 RGS family.

RESULTS

Elimination of Gβ5-RGS complexes led to a striking level of hyperactivity that far exceeds activity levels previously observed in animal models. This hyperactivity was accompanied by motor learning deficits and paradoxical behavioral sensitization to a novel environment. Neurochemical studies indicated that Gβ5-RGS-deficient mice had higher sensitivity of inhibitory GPCR signaling and deficits in basal levels, release, and reuptake of dopamine. Surprisingly, pharmacological treatment with monoamine reuptake inhibitors failed to alter hyperactivity. In contrast, blockade of NMDA receptors reversed the expression of hyperactivity in Gβ5-RGS-deficient mice.

CONCLUSIONS

These findings establish that Gβ5-RGS complexes are critical regulators of monoamine-NMDA receptor signaling cross-talk and link these complexes to disorders that manifest as hyperactivity, impaired learning, and motor dysfunctions.

CaMKII binding to GluN2B is critical during memory consolidation

Memory is essential for our normal daily lives and our sense of self. Ca(2+) influx through the NMDA-type glutamate receptor (NMDAR) and the ensuing activation of the Ca(2+) and calmodulin-dependent protein kinase (CaMKII) are required for memory formation and its physiological correlate, long-term potentiation (LTP). The Ca(2+) influx induces CaMKII binding to the NMDAR to strategically recruit CaMKII to synapses that are undergoing potentiation. We generated mice with two point mutations that impair CaMKII binding to the NMDAR GluN2B subunit. Ca(2+)-triggered postsynaptic accumulation is largely abrogated for CaMKII and destabilized for TARPs, which anchor AMPA-type glutamate receptors (AMPAR). LTP is reduced by 50% and phosphorylation of the AMPAR GluA1 subunit by CaMKII, which enhances AMPAR conductance, impaired. The mutant mice learn the Morris water maze (MWM) as well as WT but show deficiency in recall during the period of early memory consolidation. Accordingly, the activity-driven interaction of CaMKII with the NMDAR is important for recall of MWM memory as early as 24 h, but not 1-2 h, after training potentially due to impaired consolidation.

GPCR and voltage-gated calcium channels (VGCC) signaling complexes

Voltage-gated ion channels are transmembrane proteins that control nerve impulses and cell homeostasis. Signaling molecules that regulate ion channel activity and density at the plasma membrane must be specifically and efficiently coupled to these channels in order to control critical physiological functions such as action potential propagation. Although their regulation by G-protein receptor activation has been extensively explored, the assembly of ion channels into signaling complexes of GPCRs plays a fundamental role, engaging specific downstream -signaling pathways that trigger precise downstream effectors. Recent work has confirmed that GPCRs can intimately interact with ion channels and serve as -chaperone proteins that finely control their gating and trafficking in subcellular microdomains. This chapter aims to describe examples of GPCR-ion channel co-assembly, focusing mainly on signaling complexes between GPCRs and voltage-gated calcium channels.

Control of striatal signaling by g protein regulators

Signaling via heterotrimeric G proteins plays a crucial role in modulating the responses of striatal neurons that ultimately shape core behaviors mediated by the basal ganglia circuitry, such as reward valuation, habit formation, and movement coordination. Activation of G protein-coupled receptors (GPCRs) by extracellular signals activates heterotrimeric G proteins by promoting the binding of GTP to their α subunits. G proteins exert their effects by influencing the activity of key effector proteins in this region, including ion channels, second messenger enzymes, and protein kinases. Striatal neurons express a staggering number of GPCRs whose activation results in the engagement of downstream signaling pathways and cellular responses with unique profiles but common molecular mechanisms. Studies over the last decade have revealed that the extent and duration of GPCR signaling are controlled by a conserved protein family named regulator of G protein signaling (RGS). RGS proteins accelerate GTP hydrolysis by the α subunits of G proteins, thus promoting deactivation of GPCR signaling. In this review, we discuss the progress made in understanding the roles of RGS proteins in controlling striatal G protein signaling and providing integration and selectivity of signal transmission. We review evidence on the formation of a macromolecular complex between RGS proteins and other components of striatal signaling pathways, their molecular regulatory mechanisms and impacts on GPCR signaling in the striatum obtained from biochemical studies and experiments involving genetic mouse models. Special emphasis is placed on RGS9-2, a member of the RGS family that is highly enriched in the striatum and plays critical roles in drug addiction and motor control.

Decreased striatal RGS2 expression is neuroprotective in Huntington's disease (HD) and exemplifies a compensatory aspect of HD-induced gene regulation

Background

The molecular phenotype of Huntington's disease (HD) is known to comprise highly reproducible changes in gene expression involving striatal signaling genes. Here we test whether individual changes in striatal gene expression are capable of mitigating HD-related neurotoxicity.

Methodology/Principal Findings

We used protein-encoding and shRNA-expressing lentiviral vectors to evaluate the effects of RGS2, RASD2, STEP and NNAT downregulation in HD. Of these four genes, only RGS2 and RASD2 modified mutant htt fragment toxicity in cultured rat primary striatal neurons. In both cases, disease modulation was in the opposite of the predicted direction: whereas decreased expression of RGS2 and RASD2 was associated with the HD condition, restoring expression enhanced degeneration of striatal cells. Conversely, silencing of RGS2 or RASD2 enhanced disease-related changes in gene expression and resulted in significant neuroprotection. These results indicate that RGS2 and RASD2 downregulation comprises a compensatory response that allows neurons to better tolerate huntingtin toxicity. Assessment of the possible mechanism of RGS2-mediated neuroprotection showed that RGS2 downregulation enhanced ERK activation. These results establish a novel link between the inhibition of RGS2 and neuroprotective modulation of ERK activity.

Conclusions

Our findings both identify RGS2 downregulation as a novel compensatory response in HD neurons and suggest that RGS2 inhibition might be considered as an innovative target for neuroprotective drug development.

Delayed postnatal loss of P/Q-type calcium channels recapitulates the absence epilepsy, dyskinesia, and ataxia phenotypes of genomic Cacna1a mutations

Inherited loss of P/Q-type calcium channel function causes human absence epilepsy, episodic dyskinesia, and ataxia, but the molecular "birthdate" of the neurological syndrome and its dependence on prenatal pathophysiology is unknown. Since these channels mediate transmitter release at synapses throughout the brain and are expressed early in embryonic development, delineating the critical circuitry and onset underlying each of the emergent phenotypes requires targeted control of gene expression. To visualize P/Q-type Ca(2+) channels and dissect their role in neuronal networks at distinct developmental stages, we created a novel conditional Cacna1a knock-in mouse by inserting the floxed green fluorescent protein derivative Citrine into the first exon of Cacna1a and then crossed it with a postnatally expressing PCP2-Cre line for delayed Purkinje cell (PC) gene deletion within the cerebellum and sparsely in forebrain (purky). PCs in purky mice lacked P/Q-type calcium channel protein and currents within the first month after birth, displayed altered spontaneous firing, and showed impaired neurotransmission. Unexpectedly, adult purky mice exhibited the full spectrum of neurological deficits seen in mice with genomic Cacna1a ablation. Our results show that the ataxia, dyskinesia, and absence epilepsy caused by inherited disorders of the P/Q-type channel arise from signaling defects beginning in late infancy, revealing an early window of opportunity for therapeutic intervention.

A kinase anchor protein 150 (AKAP150)-associated protein kinase A limits dendritic spine density

The A kinase anchor protein AKAP150 recruits the cAMP-dependent protein kinase (PKA) to dendritic spines. Here we show that in AKAP150 (AKAP5) knock-out (KO) mice frequency of miniature excitatory post-synaptic currents (mEPSC) and inhibitory post-synaptic currents (mIPSC) are elevated at 2 weeks and, more modestly, 4 weeks of age in the hippocampal CA1 area versus litter mate WT mice. Linear spine density and ratio of AMPAR to NMDAR EPSC amplitudes were also increased. Amplitude and decay time of mEPSCs, decay time of mIPSCs, and spine size were unaltered. Mice in which the PKA anchoring C-terminal 36 residues of AKAP150 are deleted (D36) showed similar changes. Furthermore, whereas acute stimulation of PKA (2-4 h) increases spine density, prolonged PKA stimulation (48 h) reduces spine density in apical dendrites of CA1 pyramidal neurons in organotypic slice cultures. The data from the AKAP150 mutant mice show that AKAP150-anchored PKA chronically limits the number of spines with functional AMPARs at 2-4 weeks of age. However, synaptic transmission and spine density was normal at 8 weeks in KO and D36 mice. Thus AKAP150-independent mechanisms correct the aberrantly high number of active spines in juvenile AKAP150 KO and D36 mice during development.

Activity-regulated genes as mediators of neural circuit plasticity

Modifications of neuronal circuits allow the brain to adapt and change with experience. This plasticity manifests during development and throughout life, and can be remarkably long lasting. Evidence has linked activity-regulated gene expression to the long-term structural and electrophysiological adaptations that take place during developmental critical periods, learning and memory, and alterations to sensory map representations in the adult. In all these cases, the cellular response to neuronal activity integrates multiple tightly coordinated mechanisms to precisely orchestrate long-lasting, functional and structural changes in brain circuits. Experience-dependent plasticity is triggered when neuronal excitation activates cellular signaling pathways from the synapse to the nucleus that initiate new programs of gene expression. The protein products of activity-regulated genes then work via a diverse array of cellular mechanisms to modify neuronal functional properties. Synaptic strengthening or weakening can reweight existing circuit connections, while structural changes including synapse addition and elimination create new connections. Posttranscriptional regulatory mechanisms, often also dependent on activity, further modulate activity-regulated gene transcript and protein function. Thus, activity-regulated genes implement varied forms of structural and functional plasticity to fine-tune brain circuit wiring.

Resistance to age-related, normal body weight gain in RGS2 deficient mice

RGS2 (regulator of G protein signaling 2) is known to limit signals mediated via Gq- and Gs-coupled GPCRs (G protein coupled receptors), and it has been implicated in the differentiation of several cells types. The physiology of RGS2 knockout mice (rgs2(-/-)) has been studied in some detail, however, a metabolic phenotype has not previously been reported. We observed that old (21-24month) rgs2(-/-) mice weigh much less than wild-type C57BL/6 controls, and exhibit greatly reduced fat deposits, decreased serum lipids, and low leptin levels. Lower weight was evident as early as four weeks and continued throughout life. Younger adult male rgs2(-/-) mice (4-8months) were found to show similar strain-related differences as the aged animals, as well improved glucose clearance and insulin sensitivity, and enhanced beta-adrenergic and glucagon signaling in isolated hepatocytes. In addition, rgs2(-/-) pre-adipocytes had reduced levels of differentiation markers (Peroxisome proliferator-activated receptor γ (PPARγ); lipoprotein lipase (Lpl); CCAAT/enhancer binding protein α (CEBPα)) and also rgs2(-/-) white adipocytes were small relative to controls, suggesting altered adipogenesis. In wild-type animals, RGS2 mRNA was decreased in brown adipose tissue after cold exposure (7 h at 4 °C) but increased in white adipose tissue in response to a high fat diet, also suggesting a role in lipid storage. No differences between strains were detected with respect to food intake, energy expenditure, GPCR-stimulated lipolysis, or adaptive thermogenesis. In conclusion this study points to RGS2 as being an important regulatory factor in controlling body weight and adipose function.