Title: The Role of Hypoxia-Inducible Factor-2α in Intestinal Iron Absorption
Abstract: Iron deficiency and iron overload affect over a billion people worldwide.Dietary iron absorption in the small intestine is critical for the maintenance of systemic iron homeostasis.Ferroportin (FPN) is the only characterized mammalian basolateral iron exporter.Its importance in iron homeostasis is underscored by mutations found in FPN in iron overload disease, hemochromatosis.Moreover, mice with a conditional deletion of FPN in the intestine were anemic and severely iron deficient.Despite the importance of FPN in maintaining iron homeostasis, the mechanism of its regulation In Vivo is unclear.Understanding the regulation of FPN is critical to developing better therapies to improve iron deficiency and overload disorders.The present data provide the first mechanistic clues into the transcriptional regulation of FPN following changes in systemic iron requirements.A biphasic regulation of FPN during iron deficiency was observed.Rapid induction of FPN following low-iron treatment was dependent on the transcription factor hypoxia-inducible factor (HIF)-2α.Intestinal ablation of HIF-2α, but not the closely related HIF-1α homolog, abrogates FPN induction following low-iron treatment.We also show that mice that overexpress intestinal HIF-2α have a dramatic increase in FPN expression.To explore the mechanism, the FPN promoter was cloned upstream of a luciferase reporter.Performing promoter luciferase assays demonstrated that HIF-2α overepxression increased promoter activity.Also, chromatin immunoprecipitation (ChIP) assays using chromatin isolated from the duodenum of mice that overexpress HIF-2α demonstrate that HIF-2α can directly bind to the FPN promoter.Interestingly, chronic iron deprivation, led to increased FPN expression independent of transcription through increased protein stability.These data demonstrate distinct pathways by which FPN is regulated to provide a rapid and sustained response during increased systemic requirements for iron, thus providing novel mechanisms to treat hemochromatosis and anemia.