Oxygen: modulator of physiological and pathophysiological processes in the liver.

Oxygen has important functions as substrate for biochemical reactions and as modulator of gene expression. In the liver, the physiologically occurring oxygen gradient is a major effector of metabolic zonation. In addition, cross-talks between the O2 signaling and nutrient signaling chains initiate a dynamic zonation pattern. Under pathological situations, hypoxia appears to be a major determinant for liver diseases and cancer. Thereby transcription factors of the HIF family are activated whereas USF proteins have the potential to counteract HIFs. In addition, feedback mechanisms between hypoxia, HIF and the IGF axes appear to exist. Thus, the knowledge of these mechanisms may help to initiate new therapies in diseases with disturbed O2 availability.