Renal ischemia-reperfusion injury and adenosine 2A receptor-mediated tissue protection: role of macrophages

Renal ischemia-reperfusion injury and adenosine 2a receptor-mediated tissue protection: role of macrophages. Am J Physiol Renal Physiol 288: F722-F731, 2005. First published November 23, 2004;doi:10.1152/ajprenal. 00378.2004.-The role of monocytes/ macrophages in the pathogenesis of ischemia-reperfusion injury ( IRI) is unknown. We sought to determine whether activation of macrophage adenosine 2A (A(2A)) receptors (A(2A)Rs) mediates tissue protection. We subjected C57B1/6 mice infused with clodronate [dichloromethylene bisphosphonate (Cl2MBP)] to IRI (32 min of ischemia followed by 24 h of reperfusion) to deplete them of macrophages. IRI induced an elevation of plasma creatinine that was reduced with Cl2MBP (26% of control). Adoptive transfer of murine RAW 264.7 cells reconstituted injury, an effect blocked significantly by A(2A) agonists (27% of plasma creatinine from mice reconstituted with macrophages). Macrophages subjected to A(2A) knockout by small interfering RNA were adoptively transferred to macrophage-depleted mice and reconstituted injury (110% of control mice); however, the increase in plasma creatinine was blocked by A(2A) agonists (20% of vehicle treatment). Finally, the A(2A) agonist effect on IRI was blocked in macrophage-depleted A2A-knockout mice reconstituted with wildtype RAW 264.7 cells. RNase protection assays 24 h after IRI demonstrated that macrophages are required for IL-6 and TGF-beta mRNA induction. However, A(2A) agonist-mediated tissue protection is independent of IL-6 and TGF-beta mRNA. We conclude that the full extent of IRI requires macrophages and that A(2A) agonist-mediated tissue protection is independent of activation of macrophage A(2A)Rs.