To sustain life mammals have an absolute and continual requirement for oxygen, which is necessary to produce energy for normal cell survival and growth. Hence, main-tainingoxygen homeostasis is a critical requirement and mammals have evolved a wide range of cellular and phy-siological responses to adapt to changes in oxygen avail-ability. In the past few years it has become evident that the transcriptional protein complex hypoxia-inducible factor (HIF) is a key regulator of these processes.
