Adora2b Signaling on Bone Marrow Derived Cells Dampens Myocardial Ischemia-Reperfusion Injury

Background: Cardiac ischemia-reperfusion (I-R) injury represents a major cause of cardiac tissue injury. Adenosine signaling dampens inflammation during cardiac I-R. The authors investigated the role of the adenosine A2b-receptor (Adora2b) on inflammatory cells during cardiac I-R. Methods: To study Adora2b signaling on inflammatory cells, the authors transplanted wild-type (WT) bone marrow (BM) into Adora2b(-/-) mice or Adora2b(-/-) BM into WT mice. To study the role of polymorphonuclear leukocytes (PMNs), neutrophil-depleted WT mice were treated with an Adora2b agonist. After treatments, mice were exposed to 60 min of myocardial ischemia and 120 min of reperfusion. Infarct sizes and troponin I concentrations were determined by triphenyltetrazolium chloride staining and enzyme-linked immunosorbent assay, respectively. Results: Transplantation of WT BM into Adora2b(-/-) mice decreased infarct sizes by 19 +/- 4% and troponin I by 87.5 +/- 25.3 ng/ml (mean +/- SD, n = 6). Transplantation of Adora2b(-/-) BM into WT mice increased infarct sizes by 20 +/- 3% and troponin I concentrations by 69.7 +/- 17.9 ng/ml (mean +/- SD, n = 6). Studies on the reperfused myocardium revealed PMNs as the dominant cell type. PMN depletion or Adora2b agonist treatment reduced infarct sizes by 30 +/- 11% or 26 +/- 13% (mean +/- SD, n = 4); however, the combination of both did not produce additional cardioprotection. Cytokine profiling showed significantly higher cardiac tumor necrosis factor alpha concentrations in Adora2b(-/-) compared with WT mice (39.3 +/- 5.3 vs. 7.5 +/- 1.0 pg/mg protein, mean +/- SD, n = 4). Pharmacologic studies on human-activated PMNs revealed an Adora2b-dependent tumor necrosis factor alpha release. Conclusion: Adora2b signaling on BM-derived cells such as PMNs represents an endogenous cardioprotective mechanism during cardiac I-R. The authors' findings suggest that Adora2b agonist treatment during cardiac I-R reduces tumor necrosis factor alpha release of PMNs, thereby dampening tissue injury.