In previous work we have shown that T-cell derived adenosine improves cardiac healing post MI and that the adenosine A2b receptor (A2bR) was significantly up-regulated in cardiac immune cells after ischemia/reperfusion injury (Circulation. 2017). More recently, we provided evidence that A2bR modulates the expression of IL-2, IFNγ, TNFα in T cells and of IL-6 in cardiomyocytes, monocytes/macrophages, granulocytes and B cells (Am J Physiol Heart Circ Physiol. 2019). Based on these findings we now explored whether CD73 – derived adenosine formed by T cells in the post MI heart, controls the pleiotropic cytokine IL-6 by activation of A2bR.

To analyze the functional impact of T-cell derived adenosine on IL-6 formation in the infarcted heart (50 min ischemia/reperfusion), we measured 23 cytokines released into the coronary effluent perfusate from isolated hearts (Langendorff) 3 days post MI from mice with and without CD73 expressed on T cells. We found profound upregulation in the release of IL-6, IL-9, MCP-1 in infarcted wild type mice, all of which were significantly reduced in infarcted CD4CD73^-/- mice, suggesting involvement of endogenously formed adenosine. To further explore the cellular source of IL-6 we isolated cardiac T cells, B cells, granulocytes and monocytes/macrophages as well as cardiomyocytes, endothelial cells, fibroblasts and epicardium derived cells (EPDCs) on day 3 post MI and measured IL-6 expression by qPCR. While cardiomyocytes and monocytes/macrophages showed some IL-6 in wild type control mice, highest IL-6 expression after MI was found in cardiac fibroblasts and epicardium derived cells (EPDC). These findings were confirmed by single cell analysis at day 5 post MI and by RNAscope (in situ hybridization) at day 3. To study the mechanism by which A2bR signals to IL-6, we activated murine peritoneal macrophages and cardiac fibroblasts with the specific A2bR agonist BAY60-6583 and found profound induction of IL-6 secretion. This effect was fully abrogated by a specific Gq-inhibitor (FR-900359(UBO-QIC)).

Collectively our data show that adenosine formed by CD73 on T-cells is quantitatively sufficient to stimulate IL-6 secretion mainly from cardiac stromal cells (fibroblasts, EPDC) involving A2bR - mediated Gq activation.