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

Abstract

Background Cardiac ischemia-reperfusion injury (I/R) represents a major cause of cardiac tissue injury. Adenosine signaling dampens inflammation during cardiac I/R. Here, we investigated the role of the adenosine A2b-receptor (Adora2b) on inflammatory cells during cardiac I/R. Methods To study Adora2b signaling on inflammatory cells, we 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. Following treatments, mice were exposed to 60 min of myocardial ischemia and 120 min of reperfusion. Infarct sizes and Troponin-I levels were determined by triphenyltetrazolium chloride staining and ELISA, 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 levels by 69.7 ± 17.9 ng/ml (mean ± SD, n = 6). Studies on the reperfused myocardium revealed PMNs as 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 reveal further cardioprotection. Cytokine profiling showed significantly higher cardiac tumor-necrosis-factor-α levels in Adora2b−/− compared to WT mice (39.3 ± 5.3 vs. 7.5 ± 1.0 pg/mg protein, mean ± SD, n = 4). Pharmacological studies on human activated PMNs revealed an Adora2b dependent tumor-necrosis-factor-α release. Conclusion Adora2b signaling on BM-derived cells such as PMNs represents an endogenous cardioprotective mechanism during cardiac I/R. Our findings suggest that Adora2b agonist treatment during cardiac I/R reduces tumor-necrosis-factor-α release of PMNs, thereby dampening tissue injury.

Differential Tissue-Specific Function of Adora2b in Cardioprotection

“…In addition, lower levels of G-CSF, stem cell factor, IL-10 and resistin were found in Adora2b f/f - Lyz2-Cre + when comparted to controls (n=2 per group; Figure 6b). Based on the cytokine profile, we hypothesized that PMNs could be the major source of these cytokine changes (17). While Lyz2-Cre+ mice affect other bone marrow derived cells such as macrophages, they have been found to be particularly effective in deleting gene targets on PMNs in a tissue specific manner (31).…”

“…Thus, it is not surprising that protective strategies to make the heart more resistant to ischemia or limit the damage during IR are an area of intense investigations (6, 16, 17, 19, 33–38). It is accepted that a number of G protein-coupled receptors can activate cardio-protective mechanisms (32).…”

“…Although in vivo experiments have shown the cardio-protective effect of the Adora2b (11, 13, 17–20), these experiments have not dissected the major cellular targets (myocytes, endothelium, or bone-marrow derived cells) responsible for the salutary effect of Adora2b activation in different settings such as cardiac IP or IR-injury of the heart.…”

Extracellular nucleotide and nucleoside signaling in vascular and blood disease

“…In contrast to the detrimental effects of ATP signaling during ischemia and reperfusion, adenosine has been implicated via activation of the Adora2a and Adora2b in attenuating tissue inflammation and promoting ischemia tolerance (Figure 3). 30,37,60,61,72,[74][75][76][77] In addition, HIFs have been shown to dampen adenosine uptake via transcriptional repression of equilibrative adenosine transporters. A clinical trial examined the use of adenosine infusions as an adjunct to reperfusion in patients with myocardial infarction and ST-segment elevation.…”

“…Second, there are many studies implicating Adora2b signaling in tissue protection during ischemia and reperfusion injury. 30,61,72,[74][75][76] As such, Adora2b antagonists could potentially exacerbate ischemia and reperfusion injury-associated complications of sickle cell crisis.…”