Hypoxic environment is also a condition for induction of angiogenesis, as exosomal miR-23a of lung cancer cell origin directly inhibits prolyl hydroxylases PHD1 and PHD2, leading to accumulation of hypoxia-inducible factor-1 (HIF-1) in endothelial cells to enhance angiogenesis (25). The gene discussed is EGLN2; the disease is lung carcinoma.