Adenosine A2A receptor signaling attenuates LPS-induced pro-inflammatory cytokine formation of mouse macrophages by inducing the expression of DUSP1

Abstract

Adenosine is known to reduce inflammation by suppressing the activity of most immune cells. Previous studies have shown that lipopolysaccharide (LPS) stimulated mouse macrophages produce adenosine, and the adenosine A2A receptor (A2AR) signaling activated in an autocrine manner attenuates LPS-induced pro-inflammatory cytokine formation. It has been suggested that A2AR signaling inhibits LPS-induced pro-inflammatory cytokine production through a unique cAMP-dependent, but PKA- and Epac-independent signaling pathway. However, the mechanism of inhibition was not identified so far. Here we report that LPS stimulation enhances A2AR expression in mouse bone marrow derived macrophages, and loss of A2ARs results in enhanced LPS-induced pro-inflammatory response. Loss of A2ARs in A2AR null macrophages did not alter the LPS-induced NF-κB activation, but an enhanced basal and LPS-induced phosphorylation of MAP kinases (especially that of JNKs) was detected in A2AR null cells. A2AR signaling did not alter the LPS-induced phosphorylation of their upstream kinases, but by regulating adenylate cyclase activity it enhanced the expression of dual specific phosphatase (DUSP)1, a negative regulator of MAP kinases. As a result, lower basal and LPS-induced DUSP1 mRNA and protein levels can be detected in A2AR null macrophages. Silencing of DUSP1 mRNA expression resulted in higher basal and LPS-induced JNK phosphorylation and LPS-induced pro-inflammatory cytokine formation in wild type macrophages, but had no effect on that in A2AR null cells. Our data indicate that A2AR signaling regulates both basal and LPS-induced DUSP1 levels in macrophages via activating the adenylate cyclase pathway.

Adenosine Receptor Signaling Targets Both PKA and Epac Pathways to Polarize Dendritic Cells to a Suppressive Phenotype

“…Accordingly, adenosine signaling or addition of PKA and Epac together significantly increased both expression of NR4A receptors and phosphorylated and total c-Fos levels, suggesting that rather than directly interfering with phosphorylation status of major inflammatory pathways, adenosine/cAMP/ PKA-Epac signaling can regulate inflammation by increasing the expression or stabilization of negative regulators of inflammation. In accordance with our observations, Kö rö skényi et al (27) have also suggested the A2AR/cAMP pathway may not alter LPS-induced NK-kB activation in macrophages but suppresses inflammation in a cAMP-dependent manner. Interestingly, chronic deletion of A2AR pathway in this study caused an increased basal level of MAPK activation, suggesting that in the absence of inflammatory stimuli adenosine, signaling alone can have important regulatory effects in macrophage differentiation and responsiveness to subsequent inflammatory stimuli.…”

Endogenous adenosine maintains cartilage homeostasis and exogenous adenosine inhibits osteoarthritis progression

“…We and others have reported previously that A2AR stimulation inhibits NF-κB translocation in osteoclast precursors454647484950515253. Because NF-κB activation, a central event in inflammation, is critical for expression of proteins associated with chondrocyte hypertrophy and cartilage destruction we determined whether A2AR stimulation regulates nuclear translocation of NF-κB in chondrocytes as well.…”

Anti-inflammatory Mechanisms Triggered by Apoptotic Cells during Their Clearance

“…In monocytes adenosine increases the expression of the Nr4A orphan nuclear receptor which then inhibits the transcriptional activity of nuclear factor-κB (NF-κB) known to play a determining role in initiating the transcription of numerous pro-inflammatory cytokines ( 90 ). The adenosine-triggered adenylate cyclase pathway in LPS-activated macrophages, on the other hand, upregulates the expression of dual-specific phosphatase 1 that interferes with the activation of LPS-activated MAP kinases ( 91 ).…”