Hypoxia up‐regulates expression of Eph receptors and ephrins in mouse skin

ABSTRACTEph receptor tyrosine kinases and their ligands (ephrins) are key players during the development of the embryonic vasculature; however, their role and regulation in adult angiogenesis remain to be defined. Both receptors and ligands have been shown to be up‐regulated in a variety of tumors. To address the hypothesis that hypoxia is an important regulator of Ephs/ephrins expression, we developed a mouse skin flap model of hypoxia. We demonstrate that our model truly represents segmental skin hypoxia by applying four independent methods: continuous measurement of partial cutaneous oxygen tension, monitoring of tissue lactate/pyruvate ratio, time course of hypoxia‐inducible factor‐1α (HLF‐1α) induction, and localization of stabilized HIF‐1α by immunofluorescence in the hypoxic skin flap. Our experiments indicate that hypoxia up‐regulates not only HIF‐1α and vascular endothelial growth factor (VEGF) expression, but also Ephs and ephrins of both A and B subclasses in the skin. In addition, we show that in Hep3B and PC‐3 cells, the hypoxia‐induced up‐regulation of Ephs and ephrins is abrogated by small interfering RNA‐mediated down‐regulation of HIF‐1α. These novel findings shed light on the role of this versatile receptor/ligand family in adult angiogenesis. Furthermore, our model offers considerable potential for analyzing distinct mechanisms of neovascularization in gene‐targeted mice.