Endocrine Abstracts

In humans the most abundant source of 11 beta-hydroxysteroid dehydrogenase type 2 is the placenta, notably placental trophoblast. This enzyme catalyses the conversion of cortisol (F) to cortisone (E) and is thought to protect the fetus from maternal hypercortisolaemia, thereby impacting on fetal growth and development. During gestation placental trophoblast is exposed to dramatic changes in oxygen tensions ranging from ~2% - 12%, changes thought to be pivotal in stimulating angiogenesis, vascular remodelling, cell proliferation and differentiation.
To investigate the effect of oxygen tension on trophoblast 11beta-HSD2 expression and activity, specific enzyme assays and quantitative real-time PCR were employed following incubation of JEG-3 choriocarcinoma cells and primary cytotrophoblast cultures at 20%, 8%, 2% O2. Sequence analysis revealed several putative hypoxia inducible factor (HIF) binding sites in the promoter of HSD11B2. This region was investigated for oxygen related changes in gene transcription using a dual luciferase reporter system.
11beta-HSD2 activity studies revealed that at 2% and 8 % oxygen activity was significantly elevated to 77.5 +/-4.5 (mean +/- SE) pmoleE per milligram of protein per hour (P=<0.01) and 60.2 +/-2.7 P=<0.05, respectively compared to 20% oxygen (48.9 +/-2.9). Increased 11beta-HSD2 activity was also observed in JEG-3 choriocarcinoma cells; 8.4 +/-0.9 (P=<0.05) and 11.4 +/-0.6 (P=<0.01) at 8% and 2% oxygen, respectively compared to 20% (6.5 +/-1.2). Furthermore, compared to expression at 20% oxygen, 11beta-HSD2 mRNA levels increased 1.73-fold +/-0.11 P=<0.01 at 2% oxygen 1.38-fold +/-0.15 (P=<0.05) at 8% oxygen in primary cytotrophoblast. Finally, Relative luciferase activity was significantly increased from 12.8-fold +/-0.7 (mean +/-SE) to 28.4-fold +/- 2.3 (P<0.0005), at 20% and 2% oxygen respectively (N=6 in triplicate), relative to the control vector.
These data demonstrate that trophoblast responds to reduced local oxygen tension by increasing 11beta-HSD2 activity and mRNA expression. Further studies are required to identify the physiological role of these changes.