Abstract 165: Regulation of Reactive Oxygen Species Production and Reactive Oxygen Species-Related Gene Expression by Hypoxia Inducible Factor-1α
Background. Hypoxia inducible factor(HIF)-1α is a key player in the cellular response to limited O2 supply. Recent evidence indicates a role for reactive oxygen species (ROS) as signaling molecules in response to changes in oxygen tension, suggesting possible “cross talk” between the hypoxia inducible transcriptional regulation pathway and oxidative stress.
Methods. We used HIF-1α deletion mouse embryonal fibroblasts (MEFs) and cardiac myocyte HIF-1a knockout mice, as well as adenovirus HIF-1α transduced cardiac myoblasts (H9c2 cells) to explore the role of HIF-1α in control of ROS production and related gene expression at basal level and after prolonged infusion of Angiotensin II (Ang II) in vivo. Cellular ROS production was determined in cell culture and in situ on frozen heart sections. Prolonged infusion of Ang II in cardiac HIF-1α deletion mice was carried out by subcutaneous implantation of osmotic minipumps containing Ang II. Hemodynamic studies were performed after 14 days.
Results. ROS production was reduced (P<0.05) in HIF-1α null MEFs and elevated by HIF-1α overexrpession in H9c2 cells (P<0.05). We found significant differences in NADPH oxidase (Nox 1 to 4) and xanthine oxidase expression between HIF-1α null MEFs and WT controls as well as between HIF-1α overexpressing H9c2 cells and bGal overexpressing controls. Ang II infusion induced a smaller increase of superoxide in the hearts of cardiac myocyte specific HIF-1α null mice compared to controls. Ang II infusion caused significant decreases of +dp/dt and −dp/dt in control hearts and to a much lesser extent in HIF-1α knockout hearts. Ang II infusion resulted in significant elevation of systemic blood pressure in wild type mice (P<0.05) while there was no significant change in HIF-1α knockouts.
Conclusions. HIF-1α plays an important role in the control of cellular ROS levels and ROS-related gene expression. The absence of HIF-1α in cardiac myocytes may interfere with the effect of Ang II on ROS production and on cardiac function. The finding that the specific deletion of HIF-1α in cardiac myocytes reduced systemic blood pressure responses to Ang II infusion in vivo, suggests a possible HIF-1α related paracrine cardiac modulation mechanism which deserves further investigation.