Chronic in vivo hypoxia in various organs : Hypoxia-inducible factor-1α and apoptosis

Abstract We studied the in vivo persistence of hypoxia-inducible factor-1α (HIF-1α), main transducer of hypoxia, the differential response in organs exposed to the same degree of hypoxemia and the relationship with apoptosis. We measured HIF-1α (immunohistochemistry peroxidase and Western blot) and apoptosis (TUNEL) in heart, liver, kidney, gastrocnemius, and brain of rats exposed to chronic normobaric hypoxia (10% O 2 ) or normoxia (21% O 2 ) for 2 weeks. Despite same arterial O 2 pressure and increased hemoglobin concentration (219 ± 5 vs. 124 ± 4 g/L), the organs responded differently. While marked in brain, muscle, and kidney cortex, HIF-1α was undetectable in heart and liver. In kidney medulla, HIF-1α was high in both normoxia and hypoxia. By contrast, apoptosis was marked in heart, slight in kidney medulla, and undetectable in other organs. We conclude that the HIF-1α response to chronic hypoxia can be a sustained phenomenon, but not in all organs, and that apoptosis responds differently from HIF-1α.