Adenosine Augments IL-10 Production by Microglial Cells through an A2B Adenosine Receptor-Mediated Process

Abstract

Microglia are activated by pathogen-associated molecular patterns and produce pro-inflammatory cytokines, such as TNF-α, IL-6, and IL-12, and the anti-inflammatory cytokine IL-10. Adenosine is an endogenous purine nucleoside and is a ligand of four G protein-coupled adenosine receptors (ARs), which are the A1AR, A2AAR, A2BAR and A3AR. ARs have been shown to suppress TNF-α production by microglia, but their role in regulating IL-10 production has not been studied. Here, we demonstrate that adenosine augments IL-10 production by activated murine microglia while suppressing the production of pro-inflammatory cytokines. Since the order of potency of selective AR agonists in inducing IL-10 production was 5′-N-ethylcarboxamidoadenosine (NECA) > N6-(3-iodobenzyl)-adenosine-5′-N-methyluronamide (IB-MECA) > 2-chloro-N6-cyclopentyladenosine (CCPA) ≥ 2-p-(2-carboxyethyl)phenethylamino-5′-N-ethyl-carboxamidoadenosine (CGS21680), and the A2BAR antagonist MRS-1754 prevented the effect of NECA, we conclude that the stimulatory effect of adenosine on IL-10 production is mediated by the A2BAR. Mechanistically, adenosine augmented IL-10 mRNA accumulation by a transcriptional process. Using mutant IL-10 promoter constructs we showed that a CREB-binding region in the promoter mediated the augmenting effect of adenosine on IL-10 transcription. Chromatin immunoprecipitation analysis demonstrated that adenosine induced CREB phosphorylation at the IL-10 promoter. Silencing CREB using lentivirally delivered shRNA blocked the enhancing effect of adenosine on IL-10 production confirming a role for CREB in mediating the stimulatory effect of adenosine on IL-10 production. In addition, adenosine augmented IL-10 production by stimulating p38 MAPK. Collectively, our results establish that A2BARs augment IL-10 production by activated murine microglia.

A novel mechanism of control of NFκB activation and inflammation involving A2B adenosine receptors

“…We also consider the report of direct regulation of expression of IL-10 by NFkB (Cao et al, 2006). Our data suggest an alternative explanation of how the A 2B AR could regulate IL-10 production through A 2B AR-dependent NFkB signaling, in addition to the A 2B AR-p38-CREB pathway reported by Koscso et al (Koscsó et al, 2012).…”

Purinergic mechanisms in neuroinflammation: An update from molecules to behavior

“…On microglia, van der Putten et al reported A 1 , A 2A and A 3 receptor expression, but not A 2B (van der Putten et al, 2009), whereas a more recent report revealed the presence of the A 2B receptor on microglia, and an important role for this receptor in augmenting the production of the cytokine, IL-10 ( Koscso et al, 2012). The difficulty in ascertaining P1 subtype expression on specific cell types lies in the possible introduction of experimental artifacts from cell culture methods, detection limits associated with anatomical methods and specificity issues relating to physiological approaches using pharmacological tools.…”

β-Arrestin 2 Negatively Regulates Toll-like Receptor 4 (TLR4)-triggered Inflammatory Signaling via Targeting p38 MAPK and Interleukin 10

“…Optimal Induction of IL-10 by LPS Requires P38 MAPK Activity-MAPKs, including ERK and p38 MAPK, play a role in the regulation of IL-10 production in different systems such as TLR-triggered signals (22,23). Since ␤-arrestin 2-deficient significantly disturbed both p38 activation and IL-10 production following LPS stimulation (Figs.…”