Adenosine A2A receptors mediate tissue protection during ischemia-reperfusion injury

It has been postulated that the adenosine A2A receptor (A2AAR) is critical for adenosine-mediated tissue protection. A2AAR-mediated inhibitions of inflammatory cells and tissue protection have been demonstrated in rat and mouse models. The precise mechanisms of A2AAR-mediated tissue protection still remain unknown. The experiments presented here have attempted to identify the targets of A2AAR-mediated tissue protection in IRI by utilizing various mouse models in a genetic approach to elucidate these targets.; We first investigated A2AAR-mediated tissue protection in C57BL/6 and A2AAR KO mice subject to liver IRI. Then we identified the hematopoietic system as the major target of A2AAR-mediated protection by using bone marrow transplantation (wt/wt and ko/wt BMT mice). In these experiments, ATL-146e, a specific A2AAR agonist, protects wt/wt, but not ko/wt BMT mice.; We further identified lymphoid cells as the principal targets of A 2AAR-mediated protection by using rag1 KO mice that lack T-cells. Rag1 KO mice had less IR-induced damage than wt mice and ATL-146e produced no further protection. Therefore, we reconstituted ragl KO mice with spleen leukocytes and CD4+ T cells. Our results show that ragl KO mice regained IR-induced damage and ATL-146e attenuated this injury after adoptive transferred with an adequate number of 136, but not A2AAR KO spleen leukocytes or CD4+ T cells. This suggests that CD4+ T cells are required for A2AAR-mediated protection.; Surprisingly, ATL-146e cannot protect lethally irradiated A2AAR KO mice repopulated with wt B6 marrow cells (wt/ko BMT mice) from liver IRI. However, this may be due to the fact that T cell replacement is only about 85% efficient. We utilized myeloid specific knockout mice (lysM+/- adora2af/f) to further explore this question. Our data show that lysM+/-adora2af/f mice have much more severe IRI than wt mice but are still protected by ATL-146e, consistent with a major role by T cells in tissue protection.; Taken together, we conclude that CD4+ T cells are necessary for A2AAR-mediated protection. We hypothesize that in order to effectively abrogate neutrophil infiltration and subsequent tissue damage, ATL-146e acts on CD4+ T cells to inhibit cytokine/chemokine release and indirectly reduce neutrophil adherence to the endothelium.