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Tissue- and Site-Specific Gene Expression of Type 2 17ß-Hydroxysteroid Dehydrogenase: In Situ Hybridization and Specific Enzymatic Activity Studies in Human Placental Endothelial Cells of the Arterial System¹

Laboratory of Ontogeny and Reproduction, Laval University Medical Center, CHUQ (M.B., P.E.P., R.D., Y.T.); Department of Obstetrics and Gynecology, Faculty of Medicine and CRBR, Laval University (Y.T.), Québec, Canada G1V 4G2; and Department of Obstetrics and Gynecology, HealthPartners Regions Hospital (C.H.B., P.D.), St. Paul, Minnesota 55101

Address all correspondence and requests for reprints to: Dr. Yves Tremblay, Laboratory of Ontogeny and Reproduction, Laval University Medical Center, CHUQ, Québec, Canada G1V 4G2. E-mail: Yves.Tremblay{at}crchul.ulaval.ca

Progesterone and estradiol are the most potent human sex steroid hormones of placental origin and are essential to the maintenance of pregnancy, the timing of parturition, the maturation of many fetal organs, and the preparation of the maternal reproductive system. Naturally, regulatory mechanisms must be in place to coordinate the synthesis and inactivation of these two hormones. We have previously shown that the highest levels of type 1 and type 2 17ß-hydroxysteroid dehydrogenase (17ßHSD) messenger ribonucleic acids (mRNAs) occur in the placenta, particularly in the villi. However, in contrast to type 1 17ßHSD mRNA, type 2 17ßHSD mRNA was not detectable in cell cultures of human cytotrophoblasts or syncytiotrophoblasts. Using in situ hybridization, we unequivocally identified endothelial cells as the only cell type expressing the type 2 17ßHSD gene in fetal villi. Moreover, type 2 17ßHSD mRNA was specifically detected in the endothelial cells of the arterial system, and at higher levels in the villi compared with endothelial cells of the cord arteries when the two tissue sections were cohybridized. In fact, both mRNA levels and enzymatic activity are at their highest levels in arterial endothelial cells. In conclusion, the endothelial cells of the villous arterioles are the primary site of type 2 17ßHSD gene expression. This suggests a regulatory role for these cells in the control of progestin, androgen, and estrogen levels during pregnancy, thus opening a whole new way of viewing regionalization and localization of steroidogenesis in the human villi.

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