Effect of glucose and oxygen deprivation on heme oxygenase expression in human chorionic villi explants and immortalized trophoblast cells

Although hypoxia induces heme oxygenase (HO)-1 mRNA and protein expression in many cell types, recent studies in our laboratory using human placental tissue have shown that a preexposure to hypoxia does not affect subsequent HO enzymatic activity for optimized assay conditions (20% O-2; 0.5 mM NADPH; 25 muM methemalbumin) or HO-1 protein content. One of the consequences of impaired blood flow is glucose deprivation, which has been shown to be an inducer of HO-1 expression in HepG2 hepatoma cells. The objective of the present study was to test the effects of a 24-h preexposure to glucose-deprived medium, in 0.5 or 20% O-2, on HO protein content and enzymatic activity in isolated chorionic villi and immortalized HTR-8/SVneo first-trimester trophoblast cells. HO protein content was determined by Western blot analysis, and microsomal HO enzymatic activity was measured by assessment of the rate of CO formation. HO enzymatic activity was increased (P<0.05) in both placental models after 24-h preexposure to glucose-deficient medium in 0.5 or 20% O-2. Preexposure (24 h) in a combination of low O-2 and low glucose concentrations decreased the protein content of the HO-1 isoform by 59.6% (P<0.05), whereas preexposure (24 h) to low glucose concentration alone increased HO-2 content by 28.2% in chorionic villi explants (P<0.05). In this preparation, HO enzymatic activity correlated with HO-2 protein content (r=0.825). However, there was no correlation between HO-2 protein content and HO enzymatic activity in HTR-8/SVneo trophoblast cells preexposed to 0.5% O-2 and low glucose concentration for 24 h. These findings indicate that the regulation of HO expression in the human placenta is a complex process that depends, at least in part, on local glucose and oxygen concentrations.