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The A 2A adenosine receptor inhibits LPS‐induced TNF‐α release from murine peritoneal macrophages through a PKA‐independent pathway
Author(s) -
Kreckler Laura M.,
Auchampach John A.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a693
Subject(s) - forskolin , adenylyl cyclase , cgs 21680 , agonist , adenosine , endocrinology , medicine , adenosine a3 receptor , adenosine receptor , receptor , chemistry , cyclic adenosine monophosphate , stimulation , biology
We have previously shown that the G s protein‐coupled A 2A adenosine receptor (A 2A AR) is the primary receptor subtype responsible for mediating the actions of adenosine to inhibit TNF‐α release from murine peritoneal macrophages in response to Toll receptor‐dependent (i.e., lipopolysaccharide [LPS]) and Toll receptor‐independent stimuli. The suppressive action of adenosine on cytokine expression explains, in part, its potent anti‐inflammatory properties. The goal of this study was to examine the signaling mechanisms by which the A 2A AR inhibits TNF‐α release. Stimulation of peritoneal macrophages with the non‐selective AR agonist NECA (1 μM), the A 2A AR agonist CGS 21680 (1 μM), or the direct adenylyl cyclase activator forskolin (50 μM) increased cAMP accumulation (171.4 ± 28.1, 97.2 ± 5.7, and 594.0 ± 119.1 fmol/50,000 cells/15min, respectively), which resulted in activation of PKA as determined by increased phosphorylation of its downstream effectors CREB and ATF‐1. Interestingly, however, blockade of PKA with either H89 (10 μM) or PKI (3 μM) did not inhibit the ability of NECA or forskolin to suppress LPS‐induced TNF‐α release. The cAMP‐sensitive guanine exchange factor (Epac) that activates the small G protein Rap is also regulated by cAMP. Similar to AR stimulation with NECA, the Epac‐selective agonist 8‐CPT‐O‐Me‐cAMP inhibited LPS‐induced TNF‐α release even after blockade of PKA with H89 or PKI. We conclude that the A 2A AR inhibits TNF‐α release by a cAMP‐dependent, PKA‐independent pathway potentially involving Epac.