Extracellular
adenosine has been implicated in vascular adaptation to
hypoxia. Based on the observation that increases in intracellular
adenosine can effectively elevate extracellular
adenosine, we studied the contribution of
adenosine kinase (AK, intracellular conversion of
adenosine to
adenosine monophosphate [
AMP]) to vascular
adenosine responses. Initial in vitro studies of ambient
hypoxia revealed prominent repression of endothelial AK transcript (85% +/- 2% reduction),
protein, and function.
Transcription factor binding assays and
hypoxia inducible factor 1-alpha (HIF-1alpha) loss- and gain-of-function studies suggested a role for HIF-1alpha in transcriptional repression of AK. Moreover, repression of AK by ambient
hypoxia was abolished in conditional HIF-1alpha mutant mice in vivo. Studies of endothelial barrier function revealed that inhibition or
siRNA repression of AK is associated with enhanced
adenosine-dependent barrier responses in vitro. Moreover, in vivo studies of vascular barrier function demonstrated that AK inhibition with
5'-iodotubericidin (1 mg/kg prior to
hypoxia) significantly attenuated
hypoxia-induced vascular leakage in multiple organs and reduced
hypoxia-associated increases in lung water. Taken together, our data reveal a critical role of AK in modulating vascular
adenosine responses and suggest pharmacologic inhibitors of AK in the treatment of conditions associated with
hypoxia-induced vascular leakage (eg,
sepsis or
acute lung injury).