Trauma-Hemorrhage and Hypoxia Differentially Influence Kupffer Cell Phagocytic Capacity: Role of Hypoxia-Inducible-Factor-1α and Phosphoinositide 3-Kinase/Akt Activation

Abstract

We investigated whether Kupffer cell phagocytosis is differentially regulated following hypoxia (by breathing hypoxic gas) and trauma-hemorrhage. We hypothesized that the differences might result from a differential activation of hypoxia-inducible factor (HIF)-1α and phosphoinositide 3-kinase (PI3K)/Akt pathway under those conditions.

HIF-1α is a biologic O2 sensor enabling adaptation to hypoxia. Studies have shown that under hypoxic conditions, HIF-1α enhances macrophage phagocytosis. Trauma-hemorrhage also produces a hypoxic insult with HIF-1α activation; however, macrophage phagocytosis is suppressed under those conditions. Thus, signaling molecules other than HIF-1α should be taken into consideration in the regulation of macrophage phagocytosis following cellular hypoxia or trauma-hemorrhage.

Male C3H/HeN mice were subjected to sham operation, trauma-hemorrhage (laparotomy, 90 minutes hemorrhagic shock, MAP 35 ± 5 mm Hg followed by resuscitation) or hypoxia (5% O2 for 120 minutes). The trauma-hemorrhage and hypoxia groups received Wortmannin (PI3K inhibitor), YC-1 (HIF-1α inhibitor) or vehicle at the time of maximum bleedout in the trauma-hemorrhage group or at a PaO2 of 30 mm Hg during hypoxic air inhalation. Mice were killed 2 hours later and samples/cells collected.

While the systemic and Kupffer cell hypoxic states were similar in the trauma-hemorrhage and hypoxia groups, phagocytic capacity was suppressed following trauma-hemorrhage but enhanced in the hypoxia group. Kupffer cells from both groups showed increased HIF-1α activation, which was prevented by Wortmannin or YC-1 treatment. The increase in Kupffer cell phagocytosis following hypoxemia was also prevented by Wortmannin or YC-1 treatment. Akt activation was suppressed in the trauma-hemorrhage group, but enhanced in the hypoxia group. Wortmannin and YC-1 treatment prevented the increase in Akt activation.

These findings indicate that the suppression of Kupffer cell phagocytosis following trauma-hemorrhage is independent of cellular hypoxia and activation of HIF-1α, but it is possibly related to suppression of the Akt activation.