Novel roles of hypoxia response system in glucose metabolism and obesity.

Oxygen is essential for ATP production in mitochondria through oxidative phosphorylation. Metazoans are equipped with the hypoxia response system that includes hypoxia-inducible factor (HIF), prolyl hydroxylase domain protein (PHD), and von Hippel-Lindau ubiquitin ligase system to combat or adapt hypoxic conditions. PHD is an oxygen-sensing enzyme that is responsible for HIF-α hydroxylation and subsequent proteasomal degradation at normoxic conditions. In hypoxic conditions, PHD activity is inhibited and transcriptional activity of HIF is increased, resulting in the induction of a broad range of genes that are involved in glucose metabolism, angiogenesis, and erythropoiesis. A worldwide epidemic of obesity, a critical risk factor for diabetes and cardiovascular diseases, has led to intense studies on adipose tissue biology, which revealed that adipose tissue functions as an endocrine organ that affects the whole body. Recent studies also suggest that inflammation and hypoxia of adipose tissue that occur as adipose tissue mass expands play an important role in the development of insulin resistance, in which PHD/HIF pathway is critically involved. The PHD/HIF pathway may be an attractive and potential target for the treatment of obesity and associated diseases.