Inflammatory Cytokines Regulate Function and Expression of Adenosine A2A Receptors in Human Monocytic THP-1 Cells

Abstract

Adenosine, acting at its receptors, particularly A2A receptors, is a potent endogenous anti-inflammatory agent that modulates the functions and differentiation of inflammatory and immune cells. Because the inflammatory milieu abounds in proinflammatory cytokines, we investigated the effects of Th1-inflammatory cytokines on function and expression of adenosine A2A receptors in the human monocytic cell line THP-1. We found that, consistent with previous reports, adenosine and 2-[p-(2-carnonylethyl)phenylethylamino]-5′-N-ethylcarboxamidoadenosine (CGS-21680), a selective A2A receptor agonist, suppress IL-12 production but increase IL-10 production in LPS-activated THP-1 cells. These effects were blocked by the A2A receptor antagonist 4-{2-[7-amino-2-(2-furyl)[1,2,4-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl}phenol (ZM-241385). More importantly, the suppressive effect of adenosine and CGS-21680 on IL-12 production was significantly enhanced in cells pretreated with either IL-1 (10 U/ml) or TNF-α (100 U/ml) but markedly attenuated in cells pretreated with IFN-γ (100 U/ml). Similarly, IL-1 and TNF-α treatment potentiated the stimulatory effect of adenosine and CGS-21680 on IL-10 production, whereas IFN-γ treatment almost completely abolished this effect. CGS-21680 stimulated an increase in intracellular cAMP in a time- and dose-dependent manner in IL-1- and TNF-α-treated cells but not in control or IFN-γ-treated cells. Both IL-1 and TNF-α increased A2A receptor mRNA and protein. In parallel with its effect on A2A receptor function, IFN-γ down-regulated A2A receptor message and protein. Because adenosine mediates many of the antiinflammatory effects of drugs such as methotrexate, these observations suggest that local changes in the cytokine milieu may influence the therapeutic response to those drugs by altering the expression and function of adenosine receptors on inflammatory cells.

Adenosine Augments IL-10 Production by Macrophages through an A2B Receptor-Mediated Posttranscriptional Mechanism

“…Stimulation of adenosine receptors has been shown to result in an anti-inflammatory, deactivated macrophage phenotype (16,17). In LPS-stimulated monocytes/macrophages, adenosine receptor activation attenuates the production of several proinflammatory cytokines, including TNF-␣ (18 -24) and IL-12 (22,25,26). In contrast to the suppressive effect of adenosine on the production of these proinflammatory mediators, adenosine up-regulates IL-10 production by LPS-stimulated monocytes/macrophages (22,26).…”

“…In LPS-stimulated monocytes/macrophages, adenosine receptor activation attenuates the production of several proinflammatory cytokines, including TNF-␣ (18 -24) and IL-12 (22,25,26). In contrast to the suppressive effect of adenosine on the production of these proinflammatory mediators, adenosine up-regulates IL-10 production by LPS-stimulated monocytes/macrophages (22,26). The mode of action of adenosine in up-regulating IL-10 production is unclear and so is the identity of receptors responsible for the adenosine enhancement of IL-10 production in LPS-activated macrophages.…”

Direct or indirect stimulation of adenosine A 2A receptors enhances bone regeneration as well as bone morphogenetic protein‐2

“…It has been reported that osteoblast function and bone formation are strongly oxygen dependent (45), and HIF regulates osteoclast-mediated bone resorption and enhances osteoclast differentiation (46) and limits the anabolic effect of parathyroid hormone (47). A2AR expression and function is also regulated by, most notably, inflammatory stimuli (48,49).…”

Adenosine in fibrosis

“…Adenosine, most likely acting at A 2A receptors, also inhibits lymphocyte proliferation and induces suppressor function and phenotype [23–34]. Occupancy of adenosine A 2A receptors on monocytes inhibits cytokine production [tumor necrosis factor-alpha (TNF- α ), interleukin (IL)-6, IL-8, and IL-12] and enhances release of the anti-inflam-matory cytokine IL-10 [14, 17, 32, 35–40]. Adenosine, acting at A 2 receptors (probably originally misidentified as A 2B receptors), inhibits inhibitory- κ B (I κ B) kinase and nuclear factor- κ B (NF κ B) translocation to the nucleus, a central step in the pathogenesis of inflammation [41, 42].…”

“…In particular, adenosine A 2A receptors on dendritic cells diminish the capacity of these cells to promote Th1-type responses [46] and diminish monocyte production of IL-12 [39, 40, 47], a central promoter of Th1 immunologic responses. Adenosine, acting through its receptors, also modulates T cell responses to antigen [32, 46, 48, 49].…”