Physiology of RGS10 in Neurons and Immune Cells

Experimental colitis promotes sustained, sex-dependent, T-cell-associated neuroinflammation and parkinsonian neuropathology

Background

The etiology of sporadic Parkinson’s disease (PD) remains uncertain, but genetic, epidemiological, and physiological overlap between PD and inflammatory bowel disease suggests that gut inflammation could promote dysfunction of dopamine-producing neurons in the brain. Mechanisms behind this pathological gut-brain effect and their interactions with sex and with environmental factors are not well understood but may represent targets for therapeutic intervention.

Methods

We sought to identify active inflammatory mechanisms which could potentially contribute to neuroinflammation and neurological disease in colon biopsies and peripheral blood immune cells from PD patients. Then, in mouse models, we assessed whether dextran sodium sulfate-mediated colitis could exert lingering effects on dopaminergic pathways in the brain and whether colitis increased vulnerability to a subsequent exposure to the dopaminergic neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We assessed the involvement of inflammatory mechanisms identified in the PD patients in colitis-related neurological dysfunction in male and female mice, utilizing mice lacking the Regulator of G-Protein Signaling 10 (RGS10)—an inhibitor of nuclear factor kappa B (NFκB)—to model enhanced NFκB activity, and mice in which CD8⁺ T-cells were depleted.

Results

High levels of inflammatory markers including CD8B and NFκB p65 were found in colon biopsies from PD patients, and reduced levels of RGS10 were found in immune cells in the blood. Male mice that experienced colitis exhibited sustained reductions in tyrosine hydroxylase but not in dopamine as well as sustained CD8⁺ T-cell infiltration and elevated Ifng expression in the brain. CD8⁺ T-cell depletion prevented colitis-associated reductions in dopaminergic markers in males. In both sexes, colitis potentiated the effects of MPTP. RGS10 deficiency increased baseline intestinal inflammation, colitis severity, and neuropathology.

Conclusions

This study identifies peripheral inflammatory mechanisms in PD patients and explores their potential to impact central dopaminergic pathways in mice. Our findings implicate a sex-specific interaction between gastrointestinal inflammation and neurologic vulnerability that could contribute to PD pathogenesis, and they establish the importance of CD8⁺ T-cells in this process in male mice.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40478-021-01240-4.

Short stature and combined immunodeficiency associated with mutations in RGS10

We report the clinical and molecular phenotype of three siblings from one family, who presented with short stature and immunodeficiency and carried uncharacterized variants in RGS10 (c.489_491del:p.E163del and c.G511T:p.A171S). This gene encodes regulator of G protein signaling 10 (RGS10), a member of a large family of GTPase-activating proteins (GAPs) that targets heterotrimeric G proteins to constrain the activity of G protein-coupled receptors, including receptors for chemoattractants. The affected individuals exhibited systemic abnormalities directly related to the RGS10 mutations, including recurrent infections, hypergammaglobulinemia, profoundly reduced lymphocyte chemotaxis, abnormal lymph node architecture, and short stature due to growth hormone deficiency. Although the GAP activity of each RGS10 variant was intact, each protein exhibited aberrant patterns of PKA-mediated phosphorylation and increased cytosolic and cell membrane localization and activity compared to the wild-type protein. We propose that the RGS10 p.E163del and p.A171S mutations lead to mislocalization of the RGS10 protein in the cytosol, thereby resulting in attenuated chemokine signaling. This study suggests that RGS10 is critical for both immune competence and normal hormonal metabolism in humans and that rare RGS10 variants may contribute to distinct systemic genetic disorders.

A broad analysis in clinical and in vitro models on regulator of G-protein signalling 10 regulation that is associated with ovarian cancer progression and chemoresistance

Ovarian cancer is one of the deadliest types of gynaecological cancers and more than half of the patients die within 5 years after diagnosis. Recurrence in advanced staged patients after chemotherapy is associated with increased chemoresistance, which results in poor prognosis. Regulator of G-protein signalling 10 (RGS10) negatively regulates cell proliferation, migration and survival by attenuating G-protein coupled-receptors mediated signalling pathways. Recent studies have shown that loss of RGS10 expression is significantly associated with proliferation and cisplatin resistance in ovarian cancer cells. SIGNIFICANCE OF THE STUDY: In this study, we analysed differential RGS10 expression levels using public microarray datasets from clinical and in vitro ovarian cancer samples. We validated that cancer progression and chemotherapy exposure change RGS10 expression. We enriched our study to evaluate the relationship between chemoresistance and differential RGS10 expression against ovarian cancer potential chemotherapeutic agent, palbociclib. Results showed that palbociclib treatment reduced cell viability, despite significantly decreased RGS10 expression in chemoresistant cells. Overall, the results confirmed that cancer progression and chemoresistance are significantly associated with the down-regulation of RGS10 while some chemotherapeutics seem to be beneficial in decreasing chemoresistance in ovarian cancer.

The Presence of High Levels of Circulating Trimethylamine N-Oxide Exacerbates Central and Peripheral Inflammation and Inflammatory Hyperalgesia in Rats Following Carrageenan Injection

Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to promote inflammation in peripheral tissues and the central nervous system (CNS), contributing to the pathogenesis of various human diseases. Here, we examined whether the presence of high levels of circulating TMAO would influence central and peripheral inflammation and inflammatory hyperalgesia in a carrageenan (CG)-induced rat model of inflammation. Rats were treated with vehicle or TMAO in drinking water. After 2 weeks of treatment, rats received intraplantar injection of saline or CG into the hind paw. Acute nociception was unaltered in TMAO-treated rats that had elevated plasma TMAO. Following CG injection, TMAO-treated rats were significantly more sensitive to thermal and mechanical stimulation of the inflamed paw and displayed greater paw edema. Molecular studies revealed that CG injection induced increases in recruitment of neutrophils/macrophages in the paw and activation of microglia in the spinal cord, along with increased activation of nuclear factor (NF)-kB and production of proinflammatory mediators in both vehicle-treated rats and TMAO-treated rats. However, the increases in the above parameters were more pronounced in TMAO-treated rats. Moreover, TMAO treatment decreased protein levels of anti-inflammatory mediator regulator of G protein signaling (RGS)-10 in both saline-injected rats and CG-injected rats. These findings suggest that the presence of high levels of circulating TMAO downregulates anti-inflammatory mediator RGS10 in both peripheral tissues and the CNS, which may increase the susceptibility to inflammatory challenge-induced NF-kB activity, leading to greater increase in production of inflammatory mediators and consequent exacerbation of peripheral inflammation and inflammatory hyperalgesia.

Gene-level genome-wide association analysis of suicide attempt, a preliminary study in a psychiatric Mexican population

Background

Evidence suggests that liability for suicide behavior is heritable; additionally, suicide has been partly related to other psychiatric disorders. Nevertheless, most of the information reported so far address Caucasian and Asian individuals. Hence, our aim was to conduct a gene‐level association study in Mexican psychiatric individuals diagnosed with suicide attempt.

Methods

We recruited 192 individuals from two clinical centers in Mexico. All participants were born in Mexico and had Mexican parents and grandparents. Direct genotyping was performed using the commercial platform Infinium PsychArray BeadChip. A p‐value lower than 1e‐05 was considered as gene‐level significant and a p‐value lower than 1e‐04 was considered as gene‐level nominal significant.

Results

Our analyses showed that SCARA5 was associated to suicide intent at a gene‐level with statistical significance (p‐value = 1.12e‐6). Other genes were nominally associated with suicide attempt: GHSR (p‐value = 0.0004), RGS10 (p‐value = 5.13e‐5), and STK33 (p‐value = 3.62e‐5). Regarding gene variant analyses, the SNPs with a statistical association (p > .05) were rs561361616, rs1537577, rs11198999 for RGS10, and rs11041981, rs11041993, rs11041994, rs11041995, rs11041997, rs10840083, rs10769918 for STK33. For these genes, previous studies have associated SCARA5 with depression, GHSR with alcohol dependence and depression, and RGS10 with schizophrenia and depression. To date, STK33 has not been associated with any psychiatric disorder.

Conclusion

Our outcomes revealed that SCARA5, GHSR, RGS10 and STK33 could be considered as risk biomarkers for suicide attempt behavior in our Mexican psychiatric sample. We recommend to perform larger scale analyses to have conclusive results.

G Protein-Coupled Receptor Systems and Their Role in Cellular Senescence

Aging is a complex biological process that is inevitable for nearly all organisms. Aging is the strongest risk factor for development of multiple neurodegenerative disorders, cancer and cardiovascular disorders. Age-related disease conditions are mainly caused by the progressive degradation of the integrity of communication systems within and between organs. This is in part mediated by, i) decreased efficiency of receptor signaling systems and ii) an increasing inability to cope with stress leading to apoptosis and cellular senescence. Cellular senescence is a natural process during embryonic development, more recently it has been shown to be also involved in the development of aging disorders and is now considered one of the major hallmarks of aging. G-protein-coupled receptors (GPCRs) comprise a superfamily of integral membrane receptors that are responsible for cell signaling events involved in nearly every physiological process. Recent advances in the molecular understanding of GPCR signaling complexity have expanded their therapeutic capacity tremendously. Emerging data now suggests the involvement of GPCRs and their associated proteins in the development of cellular senescence. With the proven efficacy of therapeutic GPCR targeting, it is reasonable to now consider GPCRs as potential platforms to control cellular senescence and the consequently, age-related 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.

14-3-3γ binds regulator of G protein signaling 14 (RGS14) at distinct sites to inhibit the RGS14:Gαi-AlF4- signaling complex and RGS14 nuclear localization

Regulator of G protein signaling 14 (RGS14) is a multifunctional brain scaffolding protein that integrates G protein and Ras/ERK signaling pathways. It is also a nucleocytoplasmic shuttling protein. RGS14 binds active Gα_i/o via its RGS domain, Raf and active H-Ras-GTP via its R1 Ras-binding domain (RBD), and inactive Gα_i1/3 via its G protein regulatory (GPR) domain. RGS14 suppresses long-term potentiation (LTP) in the CA2 region of the hippocampus, thereby regulating hippocampally based learning and memory. The 14-3-3 family of proteins is necessary for hippocampal LTP and associative learning and memory. Here, we show direct interaction between RGS14 and 14-3-3γ at two distinct sties, one phosphorylation-independent and the other phosphorylation-dependent at Ser-218 that is markedly potentiated by signaling downstream of active H-Ras. Using bioluminescence resonance energy transfer (BRET), we show that the pSer-218-dependent RGS14/14-3-3γ interaction inhibits active Gα_i1-AlF₄^- binding to the RGS domain of RGS14 but has no effect on active H-Ras and inactive Gα_i1-GDP binding to RGS14. By contrast, the phosphorylation-independent binding of 14-3-3 has no effect on RGS14/Gα_i interactions but, instead, inhibits (directly or indirectly) RGS14 nuclear import and nucleocytoplasmic shuttling. Together, our findings describe a novel mechanism of negative regulation of RGS14 functions, specifically interactions with active Gα_i and nuclear import, while leaving the function of other RGS14 domains intact. Ongoing studies will further elucidate the physiological function of this interaction between RGS14 and 14-3-3γ, providing insight into the functions of both RGS14 and 14-3-3 in their roles in modulating synaptic plasticity in the hippocampus.

Endogenous RGS14 is a cytoplasmic-nuclear shuttling protein that localizes to juxtanuclear membranes and chromatin-rich regions of the nucleus

Regulator of G protein signaling 14 (RGS14) is a multifunctional scaffolding protein that integrates G protein and H-Ras/MAPkinase signaling pathways to regulate synaptic plasticity important for hippocampal learning and memory. However, to date, little is known about the subcellular distribution and roles of endogenous RGS14 in a neuronal cell line. Most of what is known about RGS14 cellular behavior is based on studies of tagged, recombinant RGS14 ectopically overexpressed in unnatural host cells. Here, we report for the first time a comprehensive assessment of the subcellular distribution and dynamic localization of endogenous RGS14 in rat B35 neuroblastoma cells. Using confocal imaging and 3D-structured illumination microscopy, we find that endogenous RGS14 localizes to subcellular compartments not previously recognized in studies of recombinant RGS14. RGS14 localization was observed most notably at juxtanuclear membranes encircling the nucleus, at nuclear pore complexes (NPC) on both sides of the nuclear envelope and within intranuclear membrane channels, and within both chromatin-poor and chromatin-rich regions of the nucleus in a cell cycle-dependent manner. In addition, a subset of nuclear RGS14 localized adjacent to active RNA polymerase II. Endogenous RGS14 was absent from the plasma membrane in resting cells; however, the protein could be trafficked to the plasma membrane from juxtanuclear membranes in endosomes derived from ER/Golgi, following constitutive activation of endogenous RGS14 G protein binding partners using AlF4¯. Finally, our findings show that endogenous RGS14 behaves as a cytoplasmic-nuclear shuttling protein confirming what has been shown previously for recombinant RGS14. Taken together, the findings highlight possible cellular roles for RGS14 not previously recognized that are distinct from the regulation of conventional GPCR-G protein signaling, in particular undefined roles for RGS14 in the nucleus.

Regulator of G Protein Signaling 10 (Rgs10) Expression Is Transcriptionally Silenced in Activated Microglia by Histone Deacetylase Activity

RGS10 has emerged as a key regulator of proinflammatory cytokine production in microglia, functioning as an important neuroprotective factor. Although RGS10 is normally expressed in microglia at high levels, expression is silenced in vitro following activation of TLR4 receptor. Given the ability of RGS10 to regulate inflammatory signaling, dynamic regulation of RGS10 levels in microglia may be an important mechanism to tune inflammatory responses. The goals of the current study were to confirm that RGS10 is suppressed in an in vivo inflammatory model of microglial activation and to determine the mechanism for activation-dependent silencing of Rgs10 expression in microglia. We demonstrate that endogenous RGS10 is present in spinal cord microglia, and RGS10 protein levels are suppressed in the spinal cord in a nerve injury-induced neuropathic pain mouse model. We show that the histone deacetylase (HDAC) enzyme inhibitor trichostatin A blocks the ability of lipopolysaccharide (LPS) to suppress Rgs10 transcription in BV-2 and primary microglia, demonstrating that HDAC enzymes are required for LPS silencing of Rgs10 Furthermore, we used chromatin immunoprecipitation to demonstrate that H3 histones at the Rgs10 proximal promoter are deacetylated in BV-2 microglia following LPS activation, and HDAC1 association at the Rgs10 promoter is enhanced following LPS stimulation. Finally, we have shown that sphingosine 1-phosphate, an endogenous microglial signaling mediator that inhibits HDAC activity, enhances basal Rgs10 expression in BV-2 microglia, suggesting that Rgs10 expression is dynamically regulated in microglia in response to multiple signals.

RGS10 Negatively Regulates Platelet Activation and Thrombogenesis

Regulators of G protein signaling (RGS) proteins act as GTPase activating proteins to negatively regulate G protein-coupled receptor (GPCR) signaling. Although several RGS proteins including RGS2, RGS16, RGS10, and RGS18 are expressed in human and mouse platelets, the respective unique function(s) of each have not been fully delineated. RGS10 is a member of the D/R12 subfamily of RGS proteins and is expressed in microglia, macrophages, megakaryocytes, and platelets. We used a genetic approach to examine the role(s) of RGS10 in platelet activation in vitro and hemostasis and thrombosis in vivo. GPCR-induced aggregation, secretion, and integrin activation was much more pronounced in platelets from Rgs10-/- mice relative to wild type (WT). Accordingly, these mice had markedly reduced bleeding times and were more susceptible to vascular injury-associated thrombus formation than control mice. These findings suggest a unique, non-redundant role of RGS10 in modulating the hemostatic and thrombotic functions of platelets in mice. RGS10 thus represents a potential therapeutic target to control platelet activity and/or hypercoagulable states.

The impact of RGS and other G-protein regulatory proteins on Gαi-mediated signaling in immunity

Leukocyte chemoattractant receptors are members of the G-protein coupled receptor (GPCR) family. Signaling downstream of these receptors directs the localization, positioning and homeostatic trafficking of leukocytes; as well as their recruitment to, and their retention at, inflammatory sites. Ligand induced changes in the molecular conformation of chemoattractant receptors results in the engagement of heterotrimeric G-proteins, which promotes α subunits to undergo GTP/GDP exchange. This results in the functional release of βγ subunits from the heterotrimers, thereby activating downstream effector molecules, which initiate leukocyte polarization, gradient sensing, and directional migration. Pertussis toxin ADP ribosylates Gαi subunits and prevents chemoattractant receptors from triggering Gαi nucleotide exchange. The use of pertussis toxin revealed the essential importance of Gαi subunit nucleotide exchange for chemoattractant receptor signaling. More recent studies have identified a range of regulatory mechanisms that target these receptors and their associated heterotrimeric G-proteins, thereby helping to control the magnitude, kinetics, and duration of signaling. A failure in these regulatory pathways can lead to impaired receptor signaling and immunopathology. The analysis of mice with targeted deletions of Gαi isoforms as well as some of these G-protein regulatory proteins is providing insights into their roles in chemoattractant receptor signaling.