Background— Ecto-5′-nucleotidase (CD73)–dependent adenosine generation has been implicated in tissue protection during acute injury. Once generated, adenosine can activate cell-surface adenosine receptors (A 1 AR, A 2A AR, A 2B AR, A 3 AR). In the present study, we define the contribution of adenosine to cardioprotection by ischemic preconditioning. Methods and Results— On the basis of observations of CD73 induction by ischemic preconditioning, we found that inhibition or targeted gene deletion of cd73 abolished infarct size-limiting effects. Moreover, 5′-nucleotidase treatment reconstituted cd73 −/− mice and attenuated infarct sizes in wild-type mice. Transcriptional profiling of adenosine receptors suggested a contribution of A 2B AR because it was selectively induced by ischemic preconditioning. Specifically, in situ ischemic preconditioning conferred cardioprotection in A 1 AR −/− , A 2A AR −/− , or A 3 AR −/− mice but not in A 2B AR −/− mice or in wild-type mice after inhibition of the A 2B AR. Moreover, A 2B AR agonist treatment significantly reduced infarct sizes after ischemia. Conclusions— Taken together, pharmacological and genetic evidence demonstrate the importance of CD73-dependent adenosine generation and signaling through A 2B AR for cardioprotection by ischemic preconditioning and suggests 5′-nucleotidase or A 2B AR agonists as therapy for myocardial ischemia.

Background-Ischemic preconditioning provides strong cardioprotection from ischemia, but its molecular mechanisms remain unknown. Convincing evidence confirms a central role of hypoxia-inducible factor (HIF)-1 in mammalian oxygen homeostasis. Thus, we pursued HIF-1 as a central component of cardioprotection by ischemic preconditioning. Methods and Results-Murine studies of in situ preconditioning revealed a robust activation of cardiac HIF-1␣. Moreover, in vivo small interfering RNA repression of cardiac HIF-1␣ resulted in abolished cardioprotection by ischemic preconditioning. In contrast, pretreatment with the HIF activator dimethyloxalylglycine was associated with cardioprotection similar to that of ischemic preconditioning itself. Finally, selective small interfering RNA repression of prolylhydroxylase 2 resulted in significant activation of HIF-1␣ and attenuated myocardial infarct sizes (0.44Ϯ0.09-fold). As an end point of HIF-dependent cardioprotection, we defined the role of A2B adenosine receptor (A2BAR)