Abstract
The nucleoside adenosine is a potent regulator of vascular homeostasis, but it remains unclear how expression or function of the adenosine‐metabolizing enzyme adenosine kinase (ADK) and the intracellular adenosine levels influence angiogenesis. We show here that hypoxia lowered the expression of ADK and increased the levels of intracellular adenosine in human endothelial cells. Knockdown (KD) of ADK elevated intracellular adenosine, promoted proliferation, migration, and angiogenic sprouting in human endothelial cells. Additionally, mice deficient in endothelial ADK displayed increased angiogenesis as evidenced by the rapid development of the retinal and hindbrain vasculature, increased healing of skin wounds, and prompt recovery of arterial blood flow in the ischemic hindlimb. Mechanistically, hypomethylation of the promoters of a series of pro‐angiogenic genes, especially for VEGFR2 in ADK KD cells, was demonstrated by the Infinium methylation assay. Methylation‐specific PCR, bisulfite sequencing, and methylated DNA immunoprecipitation further confirmed hypomethylation in the promoter region of VEGFR2 in ADK‐deficient endothelial cells. Accordingly, loss or inactivation of ADK increased VEGFR2 expression and signaling in endothelial cells. Based on these findings, we propose that ADK downregulation‐induced elevation of intracellular adenosine levels in endothelial cells in the setting of hypoxia is one of the crucial intrinsic mechanisms that promote angiogenesis.
Synopsis
HIF‐dependent adenosine kinase (ADK) downregulation in endothelial cells under hypoxia elevates intracellular adenosine thereby inducing DNA hypomethylation, increasing VEGFR2 expression and promoting angiogenesis.
Hypoxia downregulates ADK and elevates intracellular adenosine in endothelial cells in a HIF‐1α and HIF‐2α‐dependent manner.
The increased level of intracellular adenosine under ADK deficiency induces DNA hypomethylation, especially of the VEGFR2 promoter.
ADK deficiency increases VEGFR2 expression and signaling in endothelial cells.
Disruption of ADK expression in endothelial cells results in faster recovery of arterial blood flow in the hindlimb ischemia mouse model.
HIF‐dependent adenosine kinase (ADK) downregulation in endothelial cells under hypoxia elevates intracellular adenosine thereby inducing DNA hypomethylation, increasing VEGFR2 expression and promoting angiogenesis.