Regulator of G-protein signaling 6 (RGS6) promotes anxiety and depression by attenuating serotonin-mediated activation of the 5-HT(1A) receptor-adenylyl cyclase axis

Low-level brain somatic mutations in exonic regions are collectively implicated in autism with germline mutations in autism risk genes

Low-level somatic mutations in the human brain are implicated in various neurological disorders. The contribution of low-level brain somatic mutations to autism spectrum disorder (ASD), however, remains poorly understood. Here, we performed high-depth exome sequencing with an average read depth of 559.3x in 181 cortical, cerebellar, and peripheral tissue samples to identify brain somatic single nucleotide variants (SNVs) in 24 ASD subjects and 31 controls. We detected ~2.4 brain somatic SNVs per exome per single brain region, with a variant allele frequency (VAF) as low as 0.3%. The mutational profiles, including the number, signature, and type, were not significantly different between the ASD patients and controls. Intriguingly, when considering genes with low-level brain somatic SNVs and ASD risk genes with damaging germline SNVs together, the merged set of genes carrying either somatic or germline SNVs in ASD patients was significantly involved in ASD-associated pathophysiology, including dendrite spine morphogenesis (p = 0.025), mental retardation (p = 0.012), and intrauterine growth retardation (p = 0.012). Additionally, the merged gene set showed ASD-associated spatiotemporal expression in the early and mid-fetal cortex, striatum, and thalamus (all p < 0.05). Patients with damaging mutations in the merged gene set had a greater ASD risk than did controls (odds ratio = 3.92, p = 0.025, 95% confidence interval = 1.12-14.79). The findings of this study suggest that brain somatic SNVs and germline SNVs may collectively contribute to ASD-associated pathophysiology.

Regulator of G protein signaling 6 (RGS6) in dopamine neurons promotes EtOH seeking, behavioral reward, and susceptibility to relapse

Mesolimbic dopamine (DA) transmission is believed to play a critical role in mediating reward responses to drugs of abuse, including alcohol (EtOH). The neurobiological mechanisms underlying EtOH-seeking behavior and dependence are not fully understood, and abstinence remains the only effective way to prevent alcohol use disorders (AUDs). Here, we developed novel RGS6fl/fl; DAT-iCreER mice to determine the role of RGS6 in DA neurons on EtOH consumption, reward, and relapse behaviors. We found that RGS6 is expressed in DA neurons in both human and mouse ventral tegmental area (VTA), and that RGS6 loss in mice upregulates DA transporter (DAT) expression in VTA DA neuron synaptic terminals. Remarkably, loss of RGS6 in DA neurons significantly reduced EtOH consumption, preference, and reward in a manner indistinguishable from that seen in RGS6-/- mice. Strikingly, RGS6 loss from DA neurons before or after EtOH behavioral reward is established significantly reduced (~ 50%) re-instatement of reward following extinguishment, demonstrating distinct roles of RGS6 in promoting reward and relapse susceptibility to EtOH. These studies identify DA neurons as the locus of RGS6 action in promoting EtOH consumption, preference, reward, and relapse. RGS6 is unique among R7 RGS proteins in promoting rather than suppressing behavioral responses to drugs of abuse and to modulate EtOH behavioral reward. This is a result of RGS6's pre-synaptic actions that we hypothesize promote VTA DA transmission by suppressing GPCR-Gαi/o-DAT signaling in VTA DA neurons. These studies identify RGS6 as a potential therapeutic target for behavioral reward and relapse to EtOH.

A splice acceptor variant in RGS6 associated with intellectual disability, microcephaly, and cataracts disproportionately promotes expression of a subset of RGS6 isoforms

Intellectual disability (ID) is associated with an increased risk of developing psychiatric disorders, suggesting a common underlying genetic factor. Importantly, altered signaling and/or expression of regulator of G protein signaling 6 (RGS6) is associated with ID and numerous psychiatric disorders. RGS6 is highly conserved and undergoes complex alternative mRNA splicing producing ~36 protein isoforms with high sequence similarity historically necessitating a global approach in functional studies. However, our recent analysis in mice revealed RGS6 is most highly expressed in CNS with RGS6L(+GGL) isoforms predominating. A previously reported genetic variant in intron 17 of RGS6 (c.1369-1G>C), associated with ID, may provide further clues into RGS6L(+GGL) isoform functional delineation. This variant was predicted to alter a highly conserved canonical 3' acceptor site creating an alternative branch point within exon 18 (included in a subset of RGS6L(+GGL) transcripts) and a frameshift forming an early stop codon. We previously identified this alternative splice site and demonstrated its use generates RGS6Lζ(+GGL) isoforms. Here, we show that the c.1369-1G>C variant disrupts the canonical, preferred (>90%) intron 17 splice site and leads to the exclusive use of the alternate exon 18 splice site, inducing disproportionate expression of a subset of isoforms, particularly RGS6Lζ(+GGL). Furthermore, RGS6 global knockout mice do not exhibit ID. Thus, ID caused by the c.1369-1G>C variant likely results from altered RGS6 isoform expression, rather than RGS6 isoform loss. In summary, these studies highlight the importance of proper RGS6 splicing and identify a previously unrecognized role of G protein signaling in ID.

Regulator of G protein signaling protein 6 alleviates acute lung injury by inhibiting inflammation and promoting cell self-renewal in mice

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a disease with high mortality and morbidity. Regulator of G protein signaling protein 6 (RGS6), identified as a tumor suppressor gene, has received increasing attention owing to its close relationship with oxidative stress and inflammation. However, the association between ARDS and RGS6 has not been reported.

METHODS

Congruously regulated G protein-coupled receptor (GPCR)-related genes and differentially expressed genes (DEGs) in an acute lung injury (ALI) model were identified, and functional enrichment analysis was conducted. In an in vivo study, the effects of RGS6 knockout were studied in a mouse model of ALI induced by lipopolysaccharide (LPS). HE staining, ELISA, and immunohistochemistry were used to evaluate pathological changes and the degree of inflammation. In vitro, qRT‒PCR, immunofluorescence staining, and western blotting were used to determine the dynamic changes in RGS6 expression in cells. The RGS6 overexpression plasmid was constructed for transfection. qRT‒PCR was used to assess proinflammatory factors transcription. Western blotting and flow cytometry were used to evaluate apoptosis and reactive oxygen species (ROS) production. Organoid culture was used to assess the stemness and self-renewal capacity of alveolar epithelial type II cells (AEC2s).

RESULTS

A total of 110 congruously regulated genes (61 congruously upregulated and 49 congruously downregulated genes) were identified among GPCR-related genes and DEGs in the ALI model. RGS6 was downregulated in vivo and in vitro in the ALI model. RGS6 was expressed in the cytoplasm and accumulated in the nucleus after LPS stimulation. Compared with the control group, we found higher mortality, more pronounced body weight changes, more serious pulmonary edema and pathological damage, and more neutrophil infiltration in the RGS6 knockout group upon LPS stimulation in vivo. Moreover, AEC2s loss was significantly increased upon RGS6 knockout. Organoid culture assays showed slower alveolar organoid formation, fewer alveolar organoids, and impaired development of new structures after passaging upon RGS6 knockout. In addition, RGS6 overexpression decreased ROS production as well as proinflammatory factor transcription in macrophages and decreased apoptosis in epithelial cells.

CONCLUSIONS

RGS6 plays a protective role in ALI not only in early inflammatory responses but also in endogenous lung stem cell regeneration.

Genes positively regulated by Mef2c in cortical neurons are enriched for common genetic variation associated with IQ and educational attainment

The myocyte enhancer factor 2 C (MEF2C) gene encodes a transcription factor important for neurogenesis and synapse development and contains common variants associated with intelligence (IQ) and educational attainment (EA). Here, we took gene expression data from the mouse cortex of a Mef2c mouse model with a heterozygous DNA binding-deficient mutation of Mef2c (Mef2c-het) and combined these data with MEF2C ChIP-seq data from cortical neurons and single-cell data from the mouse brain. This enabled us to create a set of genes that were differentially regulated in Mef2c-het mice, represented direct target genes of MEF2C and had elevated in expression in cortical neurons. We found this gene-set to be enriched for genes containing common genetic variation associated with IQ and EA. Genes within this gene-set that were down-regulated, i.e. have reduced expression in Mef2c-het mice versus controls, were specifically significantly enriched for both EA and IQ associated genes. These down-regulated genes were enriched for functionality in the adenylyl cyclase signalling system, which is known to positively regulate synaptic transmission and has been linked to learning and memory. Within the adenylyl cyclase signalling system, three genes regulated by MEF2C, CRHR1, RGS6, and GABRG3, are associated at genome-wide significant levels with IQ and/or EA. Our results indicate that genetic variation in MEF2C and its direct target genes within cortical neurons contribute to variance in cognition within the general population, and the molecular mechanisms involved include the adenylyl cyclase signalling system's role in synaptic function.

Regulator of G protein signaling 6 (RGS6) in ventral tegmental area (VTA) dopamine neurons promotes EtOH seeking, behavioral reward and susceptibility to relapse

Mesolimbic dopamine (DA) transmission is believed to play a critical role in mediating reward responses to drugs of abuse, including alcohol (EtOH). EtOH is the most abused substance worldwide with chronic consumption often leading to the development of dependence and abuse. Unfortunately, the neurobiological mechanisms underlying EtOH-seeking behavior and dependence are not fully understood, and abstinence remains the only effective way to prevent alcohol use disorders (AUDs). Here, we developed novel RGS6 fl/fl ; DAT-iCreER mice to determine the role of RGS6 in VTA DA neurons on EtOH consumption and reward behaviors. We found that RGS6 is expressed in DA neurons in both human and mouse VTA, and that RGS6 loss in mice upregulates DA transporter (DAT) expression in VTA DA neuron synaptic terminals. Remarkably, loss of RGS6 in VTA DA neurons significantly reduced EtOH consumption, preference, and reward in a manner indistinguishable from that seen in RGS6 -/- mice. Strikingly, RGS6 loss from VTA DA neurons before or after EtOH behavioral reward is established significantly reduced (∼50%) re-instatement of reward following extinguishment, demonstrating distinct roles of RGS6 in promoting reward and relapse susceptibility to EtOH. These studies illuminate a critical role of RGS6 in the mesolimbic circuit in promoting EtOH seeking, reward, and reinstatement. We propose that RGS6 functions to promote DA transmission through its function as a negative modulator of GPCR-Gα i/o -DAT signaling in VTA DA neurons. These studies identify RGS6 as a potential therapeutic target for behavioral reward and relapse to EtOH.

RGS6 negatively regulates inhibitory G protein signaling in dopamine neurons and positively regulates binge-like alcohol consumption in mice

BACKGROUND AND PURPOSE

Drugs of abuse, including alcohol, increase dopamine in the mesocorticolimbic system via actions on dopamine neurons in the ventral tegmental area (VTA). Increased dopamine transmission can activate inhibitory G protein signalling pathways in VTA dopamine neurons, including those controlled by GABAB and D2 receptors. Members of the R7 subfamily of regulator of G protein signalling (RGS) proteins can regulate inhibitory G protein signalling, but their influence on VTA dopamine neurons is unclear. Here, we investigated the influence of RGS6, an R7 RGS family memberthat has been implicated in the regulation of alcohol consumption in mice, on inhibitory G protein signalling in VTA dopamine neurons.

EXPERIMENTAL APPROACH

We used molecular, electrophysiological and genetic approaches to probe the impact of RGS6 on inhibitory G protein signalling in VTA dopamine neurons and on binge-like alcohol consumption in mice.

KEY RESULTS

RGS6 is expressed in adult mouse VTA dopamine neurons and it modulates inhibitory G protein signalling in a receptor-dependent manner, tempering D2 receptor-induced somatodendritic currents and accelerating deactivation of synaptically evoked GABAB receptor-dependent responses. RGS6-/- mice exhibit diminished binge-like alcohol consumption, a phenotype replicated in female (but not male) mice lacking RGS6 selectively in VTA dopamine neurons.

CONCLUSIONS AND IMPLICATIONS

RGS6 negatively regulates GABAB - and D2 receptor-dependent inhibitory G protein signalling pathways in mouse VTA dopamine neurons and exerts a sex-dependent positive influence on binge-like alcohol consumption in adult mice. As such, RGS6 may represent a new diagnostic and/or therapeutic target for alcohol use disorder.

RGS6 suppresses TGF-β-induced epithelial-mesenchymal transition in non-small cell lung cancers via a novel mechanism dependent on its interaction with SMAD4

Regulator of G-protein signaling 6 (RGS6) is a newly discovered tumor suppressor that has been shown to be protective in development of various cancers such as breast cancer and bladder cancer. But the mechanisms underlying these tumor-suppressing functions of RGS6 are not fully understood. Here, we discover a novel function of RGS6 in suppressing TGF-β-induced epithelial-mesenchymal transition (EMT) of non-small cell lung cancer (NSCLC) cells and in vivo NSCLC metastasis. Using both bioinformatics and experimental tools, we showed that RGS6 was downregulated in lung cancer tissues compared to noncancerous counterparts, and low expression of RGS6 was associated with poor survival of lung cancer patients. Overexpression of RGS6 suppressed TGF-β-induced EMT in vitro and TGF-β-promoted metastasis in vivo, by impairing gene expression of downstream effectors induced by the canonical TGF-β-SMAD signaling. The ability of RGS6 to suppress TGF-β-SMAD-mediated gene expression relied on its binding to SMAD4 to prevent complex formation between SMAD4 and SMAD2/3, but independent of its regulation of the G-protein signaling. Interaction between RGS6 and SMAD4 caused less nuclear entry of p-SMAD3 and SMAD4, resulting in inefficient SMAD3-mediated gene expression. Taken together, our findings reveal a novel and noncanonical role of RGS6 in regulation of TGF-β-induced EMT and metastasis of NSCLC and identify RGS6 as a prognostic marker and a potential novel target for NSCLC therapy.

Neuronal G protein-gated K+ channels

G protein-gated inwardly rectifying K⁺ (GIRK/Kir3) channels exert a critical inhibitory influence on neurons. Neuronal GIRK channels mediate the G protein-dependent, direct/postsynaptic inhibitory effect of many neurotransmitters including γ-aminobutyric acid (GABA), serotonin, dopamine, adenosine, somatostatin, and enkephalin. In addition to their complex regulation by G proteins, neuronal GIRK channel activity is sensitive to PIP₂, phosphorylation, regulator of G protein signaling (RGS) proteins, intracellular Na⁺ and Ca²⁺, and cholesterol. The application of genetic and viral manipulations in rodent models, together with recent progress in the development of GIRK channel modulators, has increased our understanding of the physiological and behavioral impact of neuronal GIRK channels. Work in rodent models has also revealed that neuronal GIRK channel activity is modified, transiently or persistently, by various stimuli including exposure drugs of abuse, changes in neuronal activity patterns, and aversive experience. A growing body of preclinical and clinical evidence suggests that dysregulation of GIRK channel activity contributes to neurological diseases and disorders. The primary goals of this review are to highlight fundamental principles of neuronal GIRK channel biology, mechanisms of GIRK channel regulation and plasticity, the nascent landscape of GIRK channel pharmacology, and the potential relevance of GIRK channels to the pathophysiology and treatment of neurological diseases and disorders.

Hepatic Regulator of G Protein Signaling 6 (RGS6) drives non-alcoholic fatty liver disease by promoting oxidative stress and ATM-dependent cell death

The pathophysiological mechanism(s) driving non-alcoholic fatty liver disease, the most prevalent chronic liver disease globally, have yet to be fully elucidated. Here, we identify regulator of G protein signaling 6 (RGS6), up-regulated in the livers of NAFLD patients, as a critical mediator of hepatic steatosis, fibrosis, inflammation, and cell death. Human patients with high hepatic RGS6 expression exhibited a corresponding high inflammatory burden, pronounced insulin resistance, and poor liver function. In mice, liver-specific RGS6 knockdown largely ameliorated high fat diet (HFD)-driven oxidative stress, fibrotic remodeling, inflammation, lipid deposition and cell death. RGS6 depletion allowed for maintenance of mitochondrial integrity restoring redox balance, improving fatty acid oxidation, and preventing loss of insulin receptor sensitivity in hepatocytes. RGS6 is both induced by ROS and increases ROS generation acting as a key amplification node to exacerbate oxidative stress. In liver, RGS6 forms a direct complex with ATM kinase supported by key aspartate residues in the RGS domain and is both necessary and sufficient to drive hyperlipidemia-dependent ATM phosphorylation. pATM and markers of DNA damage (γH2AX) were also elevated in livers from NAFLD patients particularly in samples with high RGS6 protein content. Unsurprisingly, RGS6 knockdown prevented ATM phosphorylation in livers from HFD-fed mice. Further, RGS6 mutants lacking the capacity for ATM binding fail to facilitate palmitic acid-dependent hepatocyte apoptosis underscoring the importance of the RGS6-ATM complex in hyperlipidemia-dependent cell death. Inhibition of RGS6, then, may provide a viable means to prevent or reverse liver damage by mitigating oxidative liver damage.

RGS6 Mediates Effects of Voluntary Running on Adult Hippocampal Neurogenesis

Voluntary running enhances adult hippocampal neurogenesis, with consequences for hippocampal-dependent learning ability and mood regulation. However, the underlying mechanism remains unclear. Here, we show that voluntary running induces unique and dynamic gene expression changes specifically within the adult-born hippocampal neurons, with significant impact on genes involved in neuronal maturation and human diseases. We identify the regulator of G protein signaling 6 (RGS6) as a key factor that mediates running impact on adult-born neurons. RGS6 overexpression mimics the positive effects of voluntary running on morphological and physiological maturation of adult new neurons and reduced sensitivity of adult-born neurons to the inhibitory effect of GABA_B (γ-Aminobutyric acid B) receptor activation. Knocking down RGS6 abolishes running-enhanced neuronal maturation and hippocampal neurogenesis-dependent learning and anxiolytic effect. Our study provides a data resource showing genome-wide intrinsic molecular changes in adult-born hippocampal neurons that contribute to voluntary running-induced neurogenesis.

Striatal RGS7 Regulates Depression-Related Behaviors and Stress-Induced Reinstatement of Cocaine Conditioned Place Preference

The striatum plays a key role in both reward-related and affective behaviors and disruptions to this circuit contributes to depression and drug addiction. However, our understanding of the molecular factors that facilitate and modify these processes are incomplete. Striatal function is modulated by G-protein-coupled receptors (GPCRs) that process vast neuromodulatory inputs. GPCR signaling is negatively regulated by regulator of G-protein signaling (Rgs) proteins. In this study, we examine the role of striatal Rgs proteins in depressive-like and reward-related behaviors in male mice. Using a genetic mouse model with specific elimination of Rgs7 in striatal neurons we found that these mice exhibit an anxiolytic-like and antidepressant-like phenotype. In contrast, knock-out of Rgs9, an abundant Rgs protein in the same neuronal population did not affect the behavioral outcome in the depressive-like tests. Mice lacking striatal Rgs7 did not show significant differences in cocaine-induced psychomotor activation, sensitization or conditional place preference (CPP). Interestingly, loss of Rgs7 in the striatum made mice resilient to stress-induced but not drug-induced reinstatement of cocaine CPP. Analysis of striatal proteome revealed that loss of Rgs7 selectively affected expression of several networks, most prominently including proteins involved in translation and vesicular exocytosis. Together, these findings begin to demonstrate the specific contribution of Rgs7 acting in the striatum toward depression as it relates to stress-induced reinstatement of drug use.

The Combination of Aquilaria sinensis (Lour.) Gilg and Aucklandia costus Falc. Volatile Oils Exerts Antidepressant Effects in a CUMS-Induced Rat Model by Regulating the HPA Axis and Levels of Neurotransmitters

The Aquilaria sinensis (Lour.) Gilg (CX)-Aucklandia costus Falc. (MX) herbal pair is frequently used in traditional Chinese medicine prescriptions for treating depression. The volatile oil from CX and MX has been shown to have good pharmacological activities on the central nervous system, but its curative effect and mechanism in the treatment of depression are unclear. Therefore, the antidepressant effect of the volatile oil from CX-MX (CMVO) was studied in chronic unpredictable mild stress (CUMS) rats. The suppressive effects of CMVO (25, 50, 100 μL/kg) against CUMS-induced depression-like behavior were evaluated using the forced swimming test (FST), open field test (OFT) and sucrose preference test (SPT). The results showed that CMVO exhibited an antidepressant effect, reversed the decreased sugar preference in the SPT and prolongation of immobility time in the FST induced by CUMS, increased the average speed, time to enter the central area, total moving distance, and enhanced the willingness of rats to explore the environment in the OFT. Inhalational administration of CMVO decreased levels of adrenocorticotropic hormone and corticosterone in serum and the expression of corticotropin-releasing hormone mRNA in the hypothalamus, which indicated regulation of over-activation of the hypothalamic-pituitary-adrenal (HPA) axis. In addition, CMVO restored levels of 5-hydroxytryptamine (5-HT), dopamine, norepinephrine and acetylcholine in the hippocampus. The RT-PCR and immunohistochemistry results showed that CMVO up-regulated the expression of 5-HT_1A mRNA. This study demonstrated the antidepressant effect of CMVO in CUMS rats, which was possibly mediated via modulation of monoamine and cholinergic neurotransmitters and regulation of the HPA axis.

Regulator of G-protein signaling 5 protein protects against anxiety- and depression-like behavior

Anxiety and depression are a major health burden. Angiotensin II, via activation of angiotensin II type 1 receptor (AT1R)-mediated brain oxidative stress and inflammation may contribute to these emotional abnormalities. In this study, we investigated the role of a regulator of G-protein signaling 5 (RGS5) protein, which regulates AT1R activity, in angiotensin II-induced brain oxidative stress, inflammation and anxiety-, and depression-like behavior. We hypothesized that deletion of the RGS5 protein would worsen angiotensin II-induced anxiety- and depression-like behavior, cerebral vascular oxidative stress, and brain inflammation. Adult male wild-type and RGS5-deficient mice were implanted with osmotic minipumps delivering either vehicle (saline) or angiotensin II (1 mg/kg/d) for three weeks. Subsequently, mice were tested for locomotor activity, anxiety-like behavior (using the elevated plus maze), and depression-like behavior (using the tail suspension test). After behavioral testing, brain tissue was collected to assess oxidative stress and inflammatory proteins. RGS5 deletion resulted in anxiety-like but not depression-like behavior when compared to wild-type mice. Combined deletion of RGS5 and angiotensin II treatment did not further worsen anxiety-like behavior observed in RGS5-deficient mice. In contrast, depression-like behavior was worsened in RGS5-deficient mice treated with angiotensin II. Interestingly, RGS5 deficiency and angiotensin II treatment had no effect on cerebral vascular oxidative stress, or on expression of the inflammatory marker vascular cell adhesion molecule-1 in the brain. RGS5 deficiency was also associated with decreased blood pressure and an enhanced pressor response to angiotensin II. These data suggest that RGS5 protects against anxiety-like behavior and against angiotensin II-induced depression-like behavior.

RGS Proteins as Critical Regulators of Motor Function and Their Implications in Parkinson's Disease

Parkinson disease (PD) is a devastating, largely nonfamilial, age-related disorder caused by the progressive loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc). Release of DA from these neurons into the dorsal striatum is crucial for regulating movement and their loss causes PD. Unfortunately, the mechanisms underlying SNc neurodegeneration remain unclear, and currently there is no cure for PD, only symptomatic treatments. Recently, several regulator of G protein signaling (RGS) proteins have emerged as critical modulators of PD pathogenesis and/or motor dysfunction and dyskinesia: RGSs 4, 6, 9, and 10. Striatal RGS4 has been shown to exacerbate motor symptoms of DA loss by suppressing M₄-autoreceptor-Gα _i/o signaling in striatal cholinergic interneurons. RGS6 and RGS9 are key regulators of D₂R-Gα _i/o signaling in SNc DA neurons and striatal medium spiny neurons, respectively. RGS6, expressed in human and mouse SNc DA neurons, suppresses characteristic PD hallmarks in aged mice, including SNc DA neuron loss, motor deficits, and α-synuclein accumulation. After DA depletion, RGS9 (through its inhibition of medium spiny neuron D₂R signaling) suppresses motor dysfunction induced by L-DOPA or D₂R-selective agonists. RGS10 is highly expressed in microglia, the brain's resident immune cells. Within the SNc, RGS10 may promote DA neuron survival through the upregulation of prosurvival genes and inhibition of microglial inflammatory factor expression. Thus, RGSs 4, 6, 9, and 10 are critical modulators of cell signaling pathways that promote SNc DA neuron survival and/or proper motor control. Accordingly, these RGS proteins represent novel therapeutic targets for the treatment of PD pathology. SIGNIFICANCE STATEMENT: Parkinson disease (PD), the most common movement disorder, is a progressive neurodegenerative disease characterized by substantia nigra pars compacta (SNc) dopamine (DA) neuron loss and subsequent motor deficits. Current PD therapies only target disease motor symptomology and are fraught with side effects. Therefore, researchers have begun to explore alternative therapeutic options. Regulator of G protein signaling (RGS) proteins, whether primarily expressed in SNc DA neurons (RGS6), striatal neurons (RGSs 4 and 9), or microglia (RGS10), modulate key signaling pathways important for SNc DA neuron survival and/or proper motor control. As such, RGS proteins represent novel therapeutic targets in PD.

Regulator of G-protein signaling (RGS) proteins as drug targets: Progress and future potentials

G protein-coupled receptors (GPCRs) play critical roles in regulating processes such as cellular homeostasis, responses to stimuli, and cell signaling. Accordingly, GPCRs have long served as extraordinarily successful drug targets. It is therefore not surprising that the discovery in the mid-1990s of a family of proteins that regulate processes downstream of GPCRs generated great excitement in the field. This finding enhanced the understanding of these critical signaling pathways and provided potentially new targets for pharmacological intervention. These regulators of G-protein signaling (RGS) proteins were viewed by many as nodes downstream of GPCRs that could be targeted with small molecules to tune signaling processes. In this review, we provide a brief overview of the discovery of RGS proteins and of the gradual and continuing discovery of their roles in disease states, focusing particularly on cancer and neurological disorders. We also discuss high-throughput screening efforts that have led to the discovery first of peptide-based and then of small-molecule inhibitors targeting a subset of the RGS proteins. We explore the unique mechanisms of RGS inhibition these chemical tools have revealed and highlight the most up-to-date studies using these tools in animal experiments. Finally, we discuss the future opportunities in the field, as there are clearly more avenues left to be explored and potentials to be realized.

RGS6 and RGS7 Discriminate between the Highly Similar Gαi and Gαo Proteins Using a Two-Tiered Specificity Strategy

RGS6 and RGS7 are regulators of G protein signaling (RGS) proteins that inactivate heterotrimeric (αβγ) G proteins and mediate diverse biological functions, such as cardiac and neuronal signaling. Uniquely, both RGS6 and RGS7 can discriminate between Gα_o and Gα_i1-two similar Gα subunits that belong to the same G_i sub-family. Here, we show that the isolated RGS domains of RGS6 and RGS7 are sufficient to achieve this specificity. We identified three specific RGS6/7 "disruptor residues" that can attenuate RGS interactions toward Gα subunits and demonstrated that their insertion into a representative high-activity RGS causes a significant, yet non-specific, reduction in activity. We further identified a unique "modulatory" residue that bypasses this negative effect, specifically toward Gα_o. Hence, the exquisite specificity of RGS6 and RGS7 toward closely related Gα subunits is achieved via a two-tier specificity system, whereby a Gα-specific modulatory motif overrides the inhibitory effect of non-specific disruptor residues. Our findings expand the understanding of the molecular toolkit used by the RGS family to achieve specific interactions with selected Gα subunits-emphasizing the functional importance of the RGS domain in determining the activity and selectivity of RGS R7 sub-family members toward particular Gα subunits.

Age-dependent nigral dopaminergic neurodegeneration and α-synuclein accumulation in RGS6-deficient mice

Parkinson's is primarily a non-familial, age-related disorder caused by α-synuclein accumulation and the progressive loss of dopamine neurons in the substantia nigra pars compacta (SNc). G protein-coupled receptor (GPCR)-cAMP signaling has been linked to a reduction in human Parkinson's incidence and α-synuclein expression. Neuronal cAMP levels are controlled by GPCRs coupled to Gs or Gi/o, which increase or decrease cAMP, respectively. Regulator of G protein signaling 6 (RGS6) powerfully inhibits Gi/o signaling. Therefore, we hypothesized that RGS6 suppresses D2 autoreceptor- Gi/o signaling in SNc dopamine neurons promoting neuronal survival and reducing α-synuclein expression. Here we provide novel evidence that RGS6 critically suppresses late-age-onset SNc dopamine neuron loss and α-synuclein accumulation. RGS6 is restrictively expressed in human SNc dopamine neurons and, despite their loss in Parkinson's, all surviving neurons express RGS6. RGS6-/- mice exhibit hyperactive D2 autoreceptors with reduced cAMP signaling in SNc dopamine neurons. Importantly, RGS6-/- mice recapitulate key sporadic Parkinson's hallmarks, including: SNc dopamine neuron loss, reduced nigrostriatal dopamine, motor deficits, and α-synuclein accumulation. To our knowledge, Rgs6 is the only gene whose loss phenocopies these features of human Parkinson's. Therefore, RGS6 is a key regulator of D2R-Gi/o signaling in SNc dopamine neurons, protecting against Parkinson's neurodegeneration and α-synuclein accumulation.

Homeostatic cAMP regulation by the RGS7 complex controls depression-related behaviors

Affective disorders arise from abnormal responses of the brain to prolonged exposure to challenging environmental stimuli. Recent work identified the orphan receptor GPR158 as a molecular link between chronic stress and depression. Here we reveal a non-canonical mechanism by which GPR158 exerts its effects on stress-induced depression by the complex formation with Regulator of G protein Signaling 7 (RGS7). Chronic stress promotes membrane recruitment of RGS7 via GPR158 in the medial prefrontal cortex (mPFC). The resultant complex suppresses homeostatic regulation of cAMP by inhibitory GPCRs in the region. Accordingly, RGS7 loss in mice induces an antidepressant-like phenotype and resiliency to stress, whereas its restoration within the mPFC is sufficient to rescue this phenotype in a GPR158-dependent way. These findings mechanistically link the unusual orphan receptor-RGS complex to a major stress mediator, the cAMP system and suggest new avenues for pharmacological interventions in affective disorders.

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.

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.

Role of hippocampal 5-HT1A receptors in the antidepressant-like phenotype of mice expressing RGS-insensitive Gαi2 protein

A single base mutation in the Gα_i2 protein (G184S) renders this Gα subunit insensitive to the negative modulatory effects of Regulator of G-protein Signaling (RGS) proteins. Mice expressing this RGS insensitive (RGSi) variant of Gα_i2 (RGSi Gα_i2) display a spontaneous antidepressant-like phenotype that is reversible by treatment with the 5-HT1A receptor (5-HT1AR) antagonist WAY100635. Here we test the hypothesis that increased activity of 5-HT1ARs in the hippocampus of RGSi Gα_i2 knock-in mice is responsible for the expression of the observed antidepressant-like behavior. We administered the 5-HT1AR antagonist WAY100635 or the agonist 8-OH-DPAT via bilateral intra-hippocampal infusion cannulae and evaluated antidepressant-like behavior using the tail suspension test (TST). WAY100635 reversed the antidepressant-like phenotype of the RGSi Gα_i2 knock-in mice and 8-OH-DPAT produced an antidepressant-like response in wild type mice that was blocked by systemic WAY100635. Furthermore, intra-hippocampal infusion of the RGS19/4 inhibitor CCG-203769 produced an antidepressant-like effect in female mice. Ex-vivo slice recording confirmed the 5-HT1AR-mediated decrease in hippocampal CA1 pyramidal neuron excitability was enhanced in the RGSi Gα_i2 knock-in mice. There was no change in hippocampal 5-HT1AR expression as measured by ligand binding but there was a compensatory reduction in Gαi proteins. The findings demonstrate that RGS protein control of hippocampal 5-HT1AR signaling is necessary and sufficient to account for the antidepressant-like phenotype in the RGSi Gα_i2 knock-in mice and that RGS proteins highly expressed in the hippocampus should be investigated as targets for novel antidepressant therapies.

Hypersensitivity to sertraline in the absence of hippocampal 5-HT1AR and 5-HTT gene expression changes following paternal corticosterone treatment

The male germ line is capable of transmitting a legacy of stress exposure to the next generation of offspring. This transgenerational process manifests by altering offspring affective behaviours, cognition and metabolism. Paternal early life trauma causes hippocampal serotonergic dysregulation in male offspring. We previously showed a transgenerational modification to male offspring anxiety-like behaviours by treatment of adult male breeders with corticosterone (CORT) prior to mating. In the present study, we used offspring from our paternal CORT model and characterised offspring serotonergic function by examining their responses to the 5HT_1AR agonist, 8-OH-DPAT, and the selective serotonin reuptake inhibitor, sertraline. We also examined whether post-weaning environmental enrichment, a paradigm well-known to modulate serotonergic signalling in the brain, had the capacity to normalise the anxiety phenotype of male offspring. Finally, we assessed gene expression levels of 5HT_1AR and serotonin transporter in the offspring hippocampus to determine whether deficits in gene transcription contributed to the male-only anxiety phenotype. We report that male and female offspring of CORT-treated fathers are hypersensitive to sertraline but have normal hypothermic responses to 8-OH-DPAT. No deficits in htr1a and sert were found in association with paternal CORT treatment, and environmental enrichment did not rescue the anxiety phenotype of male offspring on the elevated-plus maze. These findings indicate that varying forms of paternal stress exert different effects on offspring brain serotonergic function.

Essentiality of Regulator of G Protein Signaling 6 and Oxidized Ca2+/Calmodulin-Dependent Protein Kinase II in Notch Signaling and Cardiovascular Development

Background

Congenital heart defects are the most common birth defects worldwide. Although defective Notch signaling is the major cause of mouse embryonic death from cardiovascular defects, how Notch signaling is regulated during embryonic vasculogenesis and heart development is poorly understood.

Methods and Results

Regulator of G protein signaling 6 (RGS6)^−/−/Ca²⁺/calmodulin‐dependent protein kinase II (CaMKII)^VV double mutant mice were developed by crossing RGS6^−/− mice with mice expressing an oxidation‐resistant CaMKIIδ (CaMKII^VV), and the resulting embryonic defects/lethality were investigated using E7.5 to E15.5 embryos. While loss of either RGS6 or oxidized CaMKIIδ does not alter embryogenesis, their combined loss causes defective Notch signaling, severe cardiovascular defects, and embryonic lethality (≈E10.5–11.5). Embryos lacking RGS6 and expressing oxidation‐resistant CaMKIIδ exhibit reduced myocardial wall thickness, abnormal trabeculation, and arterial specification defects. Double mutants show vascular remodeling defects, including reduced neurovascularization, delayed neural tube maturation, and small dorsal aortae. These striking cardiovascular defects were accompanied by placental and yolk sac defects in angiogenesis, hematopoiesis, and vascular remodeling similar to what is seen with defective Notch1 signaling. Double mutant hearts, embryos, and yolk sacs exhibit profound downregulation of Notch1, Jagged 1, and Notch downstream target genes Hey1, Hey2, and Hey1L as well as impaired Notch1 signaling in embryos/hearts.

Conclusions

RGS6 and oxidized CaMKIIδ together function as novel critical upstream modulators of Notch signaling required for normal cardiovascular development and embryo survival. Their combined need indicates that they function in parallel pathways needed for Notch1 signaling in yolk sac, placenta and embryos. Thus, dysregulated embryonic RGS6 expression and oxidative activation of CaMKII may potentially contribute to congenital heart defects.

Regulation of G-protein coupled receptor signalling underpinning neurobiology of mood disorders and depression

G-protein coupled receptors (GPCRs) have long been at the center of investigations of the neurobiology of depression and mood disorders. Different facets of GPCR signalling pathways, including those controlling monoaminergic and neuropeptidergic hormonal systems are believed to be dysregulated in major depressive and bipolar disorders. Although these receptors are key molecular targets for a variety of therapeutic agents and continue to be the focus of intense pharmaceutical development, the molecular mechanisms activated by these GPCRs and underpin the pathological basis of mood disorders remain poorly understood. This review will discuss some of the emerging regulatory mechanisms of GPCR signaling in the central nervous system (CNS) involving protein-protein interactions, downstream effectors and cross-talk with other signaling molecules and their potential involvement in the neurobiology of psychiatric disease.

The evolution of regulators of G protein signalling proteins as drug targets - 20 years in the making: IUPHAR Review 21

Regulators of G protein signalling (RGS) proteins are celebrating the 20th anniversary of their discovery. The unveiling of this new family of negative regulators of G protein signalling in the mid-1990s solved a persistent conundrum in the G protein signalling field, in which the rate of deactivation of signalling cascades in vivo could not be replicated in exogenous systems. Since then, there has been tremendous advancement in the knowledge of RGS protein structure, function, regulation and their role as novel drug targets. RGS proteins play an important modulatory role through their GTPase-activating protein (GAP) activity at active, GTP-bound Gα subunits of heterotrimeric G proteins. They also possess many non-canonical functions not related to G protein signalling. Here, an update on the status of RGS proteins as drug targets is provided, highlighting advances that have led to the inclusion of RGS proteins in the IUPHAR/BPS Guide to PHARMACOLOGY database of drug targets.

Development of a bimolecular luminescence complementation assay for RGS: G protein interactions in cells

Cell based assessment tools and screening platforms are the preferred paradigm for small molecule identification and validation due to selectively identifying molecules with cellular activity and validation of compound activity against target proteins in their native environment. With respect to Regulator of G Protein Signaling (RGS) proteins, current cell based methodologies are either low throughput or monitor downstream signaling consequences. The increasing number of reports indicating RGS function in various disease pathogeneses highlights the need for a robust RGS inhibitor discovery and characterization paradigm. Promega's NanoBit Protein Complementation Assay utilizes NanoLuc, an engineered luciferase with enhanced luminescence characteristics which allow for both robust and kinetic assessment of protein interaction formation and disruption. Here we characterized 15 separate RGS: G protein interactions using this system. The binding profile of RGS: Gα interactions correlates to prior published biochemical binding profiles of these proteins. Additionally, we demonstrated this system is suitable for high throughput screening efforts via calculation of Z-factors for three of the interactions and demonstrated that a known small molecule inhibitor of RGS4 disrupts the RGS4: Gα_i1 protein-protein interaction. In conclusion, the NanoBit Protein Complementation Assay holds promise as a robust platform for discovery and characterization of RGS inhibitors.

RGS proteins as targets in the treatment of intestinal inflammation and visceral pain: New insights and future perspectives

Regulators of G protein signaling (RGS) proteins provide timely termination of G protein-coupled receptor (GPCR) responses. Serving as a central control point in GPCR signaling cascades, RGS proteins are promising targets for drug development. In this review, we discuss the involvement of RGS proteins in the pathophysiology of the gastrointestinal inflammation and their potential to become a target for anti-inflammatory drugs. Specifically, we evaluate the emerging evidence for modulation of selected receptor families: opioid, cannabinoid and serotonin by RGS proteins. We discuss how the regulation of RGS protein level and activity may modulate immunological pathways involved in the development of intestinal inflammation. Finally, we propose that RGS proteins may serve as a prognostic factor for survival rate in colorectal cancer. The ideas introduced in this review set a novel conceptual framework for the utilization of RGS proteins in the treatment of gastrointestinal inflammation, a growing major concern worldwide.

RGS6 as a Novel Therapeutic Target in CNS Diseases and Cancer

Regulator of G protein signaling (RGS) proteins are gatekeepers regulating the cellular responses induced by G protein-coupled receptor (GPCR)-mediated activation of heterotrimeric G proteins. Specifically, RGS proteins determine the magnitude and duration of GPCR signaling by acting as a GTPase-activating protein for Gα subunits, an activity facilitated by their semiconserved RGS domain. The R7 subfamily of RGS proteins is distinguished by two unique domains, DEP/DHEX and GGL, which mediate membrane targeting and stability of these proteins. RGS6, a member of the R7 subfamily, has been shown to specifically modulate Gαi/o protein activity which is critically important in the central nervous system (CNS) for neuronal responses to a wide array of neurotransmitters. As such, RGS6 has been implicated in several CNS pathologies associated with altered neurotransmission, including the following: alcoholism, anxiety/depression, and Parkinson's disease. In addition, unlike other members of the R7 subfamily, RGS6 has been shown to regulate G protein-independent signaling mechanisms which appear to promote both apoptotic and growth-suppressive pathways that are important in its tumor suppressor function in breast and possibly other tissues. Further highlighting the importance of RGS6 as a target in cancer, RGS6 mediates the chemotherapeutic actions of doxorubicin and blocks reticular activating system (Ras)-induced cellular transformation by promoting degradation of DNA (cytosine-5)-methyltransferase 1 (DNMT1) to prevent its silencing of pro-apoptotic and tumor suppressor genes. Together, these findings demonstrate the critical role of RGS6 in regulating both G protein-dependent CNS pathology and G protein-independent cancer pathology implicating RGS6 as a novel therapeutic target.

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.

Two for the Price of One: G Protein-Dependent and -Independent Functions of RGS6 In Vivo

Regulator of G protein signaling 6 (RGS6) is unique among the members of the RGS protein family as it remains the only protein with the demonstrated capacity to control G protein-dependent and -independent signaling cascades in vivo. RGS6 inhibits signaling mediated by γ-aminobutyric acid B receptors, serotonin 1A receptors, μ opioid receptors, and muscarinic acetylcholine 2 receptors. RGS6 deletion triggers distinct behavioral phenotypes resulting from potentiated signaling by these G protein-coupled receptors namely ataxia, a reduction in anxiety and depression, enhanced analgesia, and increased parasympathetic tone, respectively. In addition, RGS6 possesses potent proapoptotic and growth suppressive actions. In heart, RGS6-dependent reactive oxygen species (ROS) production promotes doxorubicin (Dox)-induced cardiomyopathy, while in cancer cells RGS6/ROS signaling is necessary for activation of the ataxia telangiectasia mutated/p53/apoptosis pathway required for the chemotherapeutic efficacy of Dox. Further, by facilitating Tip60 (trans-acting regulator protein of HIV type 1-interacting protein 60 kDa)-dependent DNA methyltransferase 1 degradation, RGS6 suppresses cellular transformation in response to oncogenic Ras. The culmination of these G protein-independent actions results in potent tumor suppressor actions of RGS6 in the murine mammary epithelium. This work summarizes evidence from human genetic studies and model animals implicating RGS6 in normal physiology, disease, and the pharmacological actions of multiple drugs. Though efforts by multiple laboratories have contributed to the ever-growing RGS6 oeuvre, the pleiotropic nature of this gene will likely lead to additional work detailing the importance of RGS6 in neuropsychiatric disorders, cardiovascular disease, and cancer.

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.

Regulator of G protein signaling 6 is a critical mediator of both reward-related behavioral and pathological responses to alcohol

Alcohol is the most commonly abused drug worldwide, and chronic alcohol consumption is a major etiological factor in the development of multiple pathological sequelae, including alcoholic cardiomyopathy and hepatic cirrhosis. Here, we identify regulator of G protein signaling 6 (RGS6) as a critical regulator of both alcohol-seeking behaviors and the associated cardiac and hepatic morbidities through two mechanistically divergent signaling actions. RGS6(-/-) mice consume less alcohol when given free access and are less susceptible to alcohol-induced reward and withdrawal. Antagonism of GABA(B) receptors or dopamine D2 receptors partially reversed the reduction in alcohol consumption in RGS6(-/-) animals. Strikingly, dopamine transporter inhibition completely restored alcohol seeking in mice lacking RGS6. RGS6 deficiency was associated with alterations in the expression of genes controlling dopamine (DA) homeostasis and a reduction in DA levels in the striatum. Taken together, these data implicate RGS6 as an essential regulator of DA bioavailability. RGS6 deficiency also provided dramatic protection against cardiac hypertrophy and fibrosis, hepatic steatosis, and gastrointestinal barrier dysfunction and endotoxemia when mice were forced to consume alcohol. Although RGS proteins canonically function as G-protein regulators, RGS6-dependent, alcohol-mediated toxicity in the heart, liver, and gastrointestinal tract involves the ability of RGS6 to promote reactive oxygen species-dependent apoptosis, an action independent of its G-protein regulatory capacity. We propose that inhibition of RGS6 might represent a viable means to reduce alcohol cravings and withdrawal in human patients, while simultaneously protecting the heart and liver from further damage upon relapse.

Rgs6 is required for adult maintenance of dopaminergic neurons in the ventral substantia nigra

Parkinson disease (PD) is characterized by the preferential, but poorly understood, vulnerability to degeneration of midbrain dopaminergic (mDA) neurons in the ventral substantia nigra compacta (vSNc). These sensitive mDA neurons express Pitx3, a transcription factor that is critical for their survival during development. We used this dependence to identify, by flow cytometry and expression profiling, the negative regulator of G-protein signaling Rgs6 for its restricted expression in these neurons. In contrast to Pitx3^−/− mDA neurons that die during fetal (vSNc) or post-natal (VTA) period, the vSNc mDA neurons of Rgs6^−/− mutant mice begin to exhibit unilateral signs of degeneration at around 6 months of age, and by one year cell loss is observed in a fraction of mice. Unilateral cell loss is accompanied by contralateral degenerating neurons that exhibit smaller cell size, altered morphology and reduced dendritic network. The degenerating neurons have low levels of tyrosine hydroxylase (TH) and decreased nuclear Pitx3; accordingly, expression of many Pitx3 target gene products is altered, including Vmat2, Bdnf, Aldh1a1 (Adh2) and Fgf10. These low TH neurons also express markers of increased dopamine signaling, namely increased DAT and phospho-Erk1/2 expression. The late onset degeneration may reflect the protective action of Rgs6 against excessive DA signaling throughout life. Rgs6-dependent protection is thus critical for adult survival and maintenance of the vSNc mDA neurons that are most affected in PD.

The locomotor deficits associated with Parkinson disease result from the death of a specific subset of dopamine neurons in the ventral part of the midbrain. The reason for the greater sensitivity to degeneration of those, relative to other, neurons is not clear. Prior work showed that the Pitx3 transcription factor is specifically expressed in these neurons where it has a survival role during development. The present work identified a cell signaling component, Rgs6, that is also restricted to the sensitive neurons in the midbrain and that exerts a protective function, particularly late in life. While the loss of Rgs6 function may predispose or contribute to Parkinson disease, its stimulation may provide a novel therapeutic avenue to treat Parkinson disease.

Inducible forebrain-specific ablation of the transcription factor Creb during adulthood induces anxiety but no spatial/contextual learning deficits

The cyclic AMP (cAMP)-response element binding protein (CREB) is an activity-dependent transcription factor playing a role in synaptic plasticity, learning and memory, and emotional behavior. However, the impact of Creb ablation on rodent behavior is vague as e.g., memory performance of different Creb mutant mice depends on the specific type of mutation per se but additionally on the background and learning protocol differences. Here we present the first targeted ablation of CREB induced during adulthood selectively in principal forebrain neurons in a pure background strain of C57BL/6 mice. All hippocampal principal neurons exhibited lack of CREB expression. Mutant mice showed a severe anxiety phenotype in the openfield and novel object exploration test as well as in the Dark-Light Box Test, but unaltered hippocampus-dependent long-term memory in the Morris water maze and in context dependent fear conditioning. On the molecular level, CREB ablation led to CREM up regulation in the hippocampus and frontal cortex which may at least in part compensate for the loss of CREB. BDNF, a postulated CREB target gene, was down regulated in the frontal lobe but not in the hippocampus; neurogenesis remained unaltered. Our data indicate that in the adult mouse forebrain the late onset of CREB ablation can, in case of memory functionality, be compensated for and is not essential for memory consolidation and retrieval during adulthood. In contrast, the presence of CREB protein during adulthood seems to be pivotal for the regulation of emotional behavior.

5-HT1A receptor-mediated phosphorylation of extracellular signal-regulated kinases (ERK1/2) is modulated by regulator of G protein signaling protein 19

The 5-HT1A receptor is a G protein coupled receptor (GPCR) that activates G proteins of the Gαi/o family. 5-HT1A receptors expressed in the raphe, hippocampus and prefrontal cortex are implicated in the control of mood and are targets for anti-depressant drugs. Regulators of G protein signaling (RGS) proteins are members of a large family that play important roles in signal transduction downstream of G protein coupled receptors (GPCRs). The main role of RGS proteins is to act as GTPase accelerating proteins (GAPs) to dampen or negatively regulate GPCR-mediated signaling. We have shown that a mouse expressing Gαi2 that is insensitive to all RGS protein GAP activity has an anti-depressant-like phenotype due to increased signaling of postsynaptic 5-HT1A receptors, thus implicating the 5-HT1A receptor-Gαi2 complex as an important target. Here we confirm that RGS proteins act as GAPs to regulate signaling to adenylate cyclase and the mitogen-activated protein kinase (MAPK) pathway downstream of the 5-HT1A receptor, using RGS-insensitive Gαi2 protein expressed in C6 cells. We go on to use short hairpin RNA (shRNA) to show that RGS19 is responsible for the GAP activity in C6 cells and also that RGS19 acts as a GAP for 5-HT1A receptor signaling in human neuroblastoma SH-SY5Y cells and primary hippocampal neurons. In addition, in both cell types the synergy between 5-HT1A receptor and the fibroblast growth factor receptor 1 in stimulating the MAPK pathway is enhanced following shRNA reduction of RGS19 expression. Thus RGS19 may be a viable new target for anti-depressant medications.