Heme Oxygenases in Pregnancy II: HO-2 is Downregulated in Human Pathologic Pregnancies


Address reprint requests to Petra Clara Arck, Biomedizinisches Forschungszentrum, Raum 2.0549, Augustenburger Platz 1, 13353 Berlin, Germany.
E-mail: petra.arck@charite.de


Problem:  We previously reported a diminished expression of the heme-degrading enzymes heme oxygenases (HO)-1 and HO-2 in decidua and placenta from mice undergoing Th1-mediated abortion, strongly indicating the protective effect of HO in murine pregnancy maintenance. Here we investigated whether the expression of HO-1 and HO-2 is also reduced at the feto-maternal interface of pathologic human pregnancies.

Method of Study:  Immunohistochemistry was used to detect HOs expression in placental and decidual first-trimester tissue from patients with: spontaneous abortion (n = 14), choriocarcinoma (n = 14), hydatidiform mole (H-mole) (n = 12), compared with normally progressing pregnancies (n = 15). Further, we investigated early third-trimester decidual and placental tissue from patients with pre-eclampsia (n = 13) compared with fetal growth retardation (n = 14) as age-matched controls.

Results:  In first trimester tissue, we observed a significant reduction of HO-2 expression in invasive trophoblast cells, endothelial cells, and syncytiotrophoblasts in samples from patients with spontaneous abortion compared with normal pregnancy. H-mole samples showed a diminished expression of HO-2 in invasive trophoblast cells and endothelial cells in comparison with NP, whereas choriocarcinoma samples showed no significant differences compared with the control. In third trimester tissue, HO-2 was also reduced in syncytiotrophoblasts and invasive trophoblast cells from pre-eclampsia compared with samples from fetal growth retardation. HO-1 expression was diminished in all pathologies investigated; however, the differences did not reach levels of significance.

Conclusions:  Our data indicate that HOs play a crucial role in pregnancy and low expression of HO-2, as observed in pathologic pregnancies, may lead to enhanced levels of free heme at the feto-maternal interface, with subsequent upregulation of adhesion molecules, allowing enhanced inflammatory cells migration to the feto-maternal interface.