Adenosine is an extracellular signaling molecule that is generated in response to cell injury where it orchestrates tissue protection and repair. Whereas
adenosine is best known for promoting anti-inflammatory activities during acute injury responses, prolonged elevations can enhance destructive tissue remodeling processes associated with
chronic disease states. The generation of
adenosine and the subsequent activation of the
adenosine 2B receptor (A(2B)R) is an important processes in the regulation of both acute and chronic
lung disease. The goal of this study was to examine the contribution of the A(2B)R in models of
bleomycin-induced
lung injury that exhibit varying degrees of acute and chronic injury. Intratracheal
bleomycin exposure results in substantial
acute lung injury followed by progressive
fibrosis. In this model, genetic removal of the A(2B)R resulted in enhanced loss of barrier function and increased
pulmonary inflammation, with few differences in indexes of
pulmonary fibrosis. These results support an anti-inflammatory role for this receptor in this model of
acute lung injury. In contrast, systemic exposure of mice to
bleomycin resulted in modest
acute lung injury together with progressive
pulmonary fibrosis. In this model, the effects of A(2B)R removal on
acute lung injury were negligible; however, there were substantial reductions in
pulmonary fibrosis, supporting a profibrotic role for this receptor. A(2B)R-dependent regulation of
IL-6 production was identified as a potential mechanism involved in the diminished
pulmonary fibrosis seen in A(2B)R knockout mice exposed to i.p.
bleomycin. These studies highlight the distinct roles of A(2B)R signaling during acute and chronic stages of
lung injury.