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Departments of 1 Pharmacology and Toxicology, 2 Anatomy and Cell Biology, and 3 Obstetrics and Gynaecology, Queen's University, Kingston, Ontario, Canada K7L 3N6
Although hypoxia induces heme oxygenase (HO)-1 protein and mRNA expression in many cell types, hypoxia has also been shown to decrease HO-1 mRNA and protein expression. We tested the hypothesis that 24-h preexposure to hypoxia in human placental preparations suppresses HO protein expression and enzymatic function. Immortalized HTR-8/SVneo first-trimester trophoblast cells and explants of normal human chorionic villi (CV) from term placentas were cultured for 24 h in 1%, 5%, or 20% O2. HO protein levels were determined by Western blot analysis, and microsomal HO activity was measured. HO-2 protein content was decreased by 17% and 5% in human trophoblast cells after 24-h exposure to 1% and 5% O2, respectively, versus 20% O2. In contrast, HO-2 protein content in CV explants was unaffected by changes in oxygenation. HO-1 protein content, which was barely detectable in both biological systems, was not affected by changes in oxygenation. Similarly, HO enzymatic activity was unchanged in both preparations after 24-h exposure to 1%, 5%, or 20% O2. The above data do not support the hypothesis that hypoxia in the human placenta suppresses both HO protein content and HO protein function. The present observations reinforce the necessity to determine both HO protein expression and function.
heme oxygenase activity; heme oxygenase-1 expression; carbon monoxide; hypoxia; placenta
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