Adenosine receptors (AR) and
extracellular signal-regulated kinases (ERK) have been implicated in tissue protection and apoptosis regulation during
ischemia/reperfusion (I/R) injury. This study tests the hypothesis that reduction of reperfusion
lung injury after A2A AR activation is associated with attenuation of apoptosis, modulation of ERK activation, and alterations in antiapoptotic and proapoptotic
protein expression (Bcl-2 and Bax, respectively). Experiments were performed in intact-chest, spontaneously breathing cats in which the arterial branch of the left lower lung lobe was occluded for 2 h and reperfused for 3 h (I/R group). Animals were treated with the selective A2A AR agonist
ATL313 given 5 min before reperfusion alone or in combination with the selective A2A AR antagonist
ZM241385. Western blot analysis showed significant reduction in expression of Bcl-2 and increase in expression of Bax after reperfusion, compared with control lungs. Phosphorylated ERK1/2 levels were also increased after reperfusion. Compared with the I/R group,
ATL313 markedly (P < 0.01) attenuated indices of injury and apoptosis including the percentage of injured alveoli, wet-dry weight ratio,
myeloperoxidase activity, in situ
terminal deoxynucleotidyl transferase-mediated
deoxyuridine triphosphate nick end-labeling-positive cells, and
caspase 3 activity and expression. Furthermore, compared with reperfused lungs, in ATL313-pretreated lungs, Western blot analysis demonstrated substantial ERK1/2 activation, increased expression of Bcl-2, and attenuated expression of Bax. The protective effects of
ATL313 were blocked by pretreatment with
ZM241385. In summary, the present study shows that in vivo activation of A2A AR confers protection against reperfusion
lung injury. This protection is associated with decreased apoptosis and involves ERK1/2 activation and alterations in antiapoptotic Bcl-2 and proapoptotic Bax
proteins.