To investigate the relationship of HIF1alpha signaling to oxidative stress,
tissue hypoxia, angiogenesis and inflammation, female Fischer 344 rats were
irradiated to the right hemithorax with a fractionated dose of 40 Gy (8 Gy x 5
days). The lung tissues were harvested before and at 4, 6, 10, 14, 18, 22 and 26
weeks after irradiation for serial studies of biological markers, including
markers for hypoxia (HIF1alpha, pimonidazole and CA IX), oxidative stress
(8-OHdG), and angiogenesis/capillary proliferation (VEGF/CD 105), as well as
macrophage activation (ED-1) and cell signaling/fibrosis (NFkappaB, TGFbeta1),
using immunohistochemistry and Western blot analysis. HIF1alpha staining could be
observed as early as 4 weeks postirradiation and was significantly increased with
time after irradiation. Importantly, HIF1alpha levels paralleled oxidative stress
(8-OHdG), tissue hypoxia (pimonidazole and CA IX), and macrophage accumulation
consistent with inflammatory response. Moreover, changes in HIF1alpha expression
identified by immunohistochemistry assay parallel the changes in TGFbeta1, VEGF,
NFkappaB and CD 105 levels in irradiated lungs. These results support the notion
that oxidative stress and tissue hypoxia might serve as triggering signals for
HIF1alpha activity in irradiated lungs, relating to radiation-induced
inflammation, angiogenesis and fibrosis.