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

Abstract

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.

Chronic Treatment with Fluoxetine Induces Sex-Dependent Analgesic Effects and Modulates HDAC2 and mGlu2 Expression in Female Mice

“…A number of HDAC inhibitors have been tested in different pain models and it has been shown that they have analgesic effects through different mechanisms ( Chiechio et al, 2009 , 2010 ; Bai et al, 2010 ; Zhang et al, 2011 ; Denk et al, 2013 ; Matsushita et al, 2013 ; Onofrj et al, 2013 ; Ximenes et al, 2013 ; Chen et al, 2014 ; Kukkar et al, 2014 ; Zammataro et al, 2014 ; Capasso et al, 2015 ; Cao et al, 2016 ; Tao et al, 2016 ; Alqinyah et al, 2017 ; Fork et al, 2017 ; Lin et al, 2017 ). We first demonstrated that HDAC inhibitors have analgesic properties via the upregulation of the metabotropic glutamate receptor type-2 ( Chiechio et al, 2009 , 2010 ; Onofrj et al, 2013 ), an inhibitory receptor whose activation or upregulation mediates analgesia ( Chiechio et al, 2002 , 2009 , 2010 ; Onofrj et al, 2013 ; Zammataro et al, 2014 ; Chiechio, 2016 ).…”

RGS10 Regulates the Expression of Cyclooxygenase-2 and Tumor Necrosis Factor Alpha through a G Protein–Independent Mechanism

“…Loss of RGS10 in microglia amplifies production of inflammatory cytokines, such as tumor necrosis factor a (TNFa) and interleukin 1b, and enhances microglia-induced neurotoxicity triggered by the toll-like receptor (TLR) ligand lipopolysaccharide (LPS) (Lee et al, 2011). Reciprocally, activation of microglia by LPS induces epigenetic silencing of RGS10, which we predict serves to amplify inflammatory signaling (Alqinyah et al, 2017). In addition to its anti-inflammatory role in microglia, RGS10 also regulates survival of ovarian cancer cells, and loss of RGS10 induces chemoresistance in ovarian cancer cells (Hooks et al, 2010;Ali et al, 2013).…”

“…Microglial RGS10 suppresses the release of TNFa and other inflammatory cytokines following inflammatory triggers (Lee et al, 2008) and plays a protective role against microglia-induced neurodegeneration of dopaminergic neurons (Lee et al, 2011). Reciprocally, microglial activation by either LPS or TNFa suppresses the expression of RGS10 and reduces RGS10 protein levels by approximately 50%-70% for approximately 48 hours (Alqinyah et al, 2017). Thus, endogenous RGS10 silencing mechanisms likely serve to amplify and enhance inflammation in a feed-forward mechanism that sustains a continuous cycle of RGS10 suppression and enhanced production of inflammatory cytokines (Lee et al, 2008;Alqinyah et al, 2017).…”

“…Thus, endogenous RGS10 silencing mechanisms likely serve to amplify and enhance inflammation in a feed-forward mechanism that sustains a continuous cycle of RGS10 suppression and enhanced production of inflammatory cytokines (Lee et al, 2008;Alqinyah et al, 2017). Importantly, the magnitude and duration of RGS10 suppression induced by transient siRNA transfection recapitulates that observed during suppression of RGS10 expression induced by endogenous activation of microglia (Alqinyah et al, 2017), suggesting that the effects reported here following siRNA knockdown will likely serve to amplify the magnitude of COX-2 and PGE 2 signaling during endogenous microglial activation.…”

Regulators of G Protein Signaling in Analgesia and Addiction

“…Liu, Chatterjee, & Fisher, 2002;Martin-McCaffrey et al, 2005;Nixon, Grenningloh, & Casey, 2002;Sivori et al, 2019) and cell proliferation (Chi et al, 2017;Madrigal et al 2017;Scherer, Cain, Kanai, Kaltenbronn, & Blumer, 2017;Tso et al, 2010;Vivot et al 2016;Willard et al, 2007;Yang and Li 2007). Members of the RGS family may additionally regulate transcriptional pathways (Alqinyah et al, 2017;Feigin and Malbon 2007;Gaspari et al, 2018;Ikeda et al, 1998;Shimizu et al 2003;Z. Liu & Fisher, 2004) and chromatin function (Alqinyah et al, 2017;Branch & Hepler, 2017;Z.…”