Expression pattern of osteopontin (OPN) in the human placenta – correlation with expression of the adhesion molecule CEACAM1

The human placenta is a complex tissue with multiple endocrine and nutritional functions and a unique capacity for rapid proliferation but tightly controlled invasion, differentiating it from malignant tumors. The cytokine osteopontin (OPN) is a glycoprotein of the extracellular matrix which has been shown to mediate cellular migration and invasion and to contribute to tumorigenesis in several types of cancers. OPN could thus also be implicated in regulating implantation and placentation by promoting cellular migration and invasion in a placenta-specific fashion. The expression pattern and cell-type specific localization of OPN in the human placenta has not been described so far. CEACAM1 is an adhesion molecule which we have recently found to be expressed at the maternal-fetal interface with a localization to the extravillous (invasive) trophoblast and to be potentially implicated in trophoblast invasion. Both OPN and CEACAM1 have been shown to interact with integrin beta3. In the present study, immunohistochemistry with specific antibodies was performed to investigate the expression pattern and cell-type specific localization of OPN in the human placenta, and to correlate it with the expression of CEACAM1. Parallel sections of 50 normal placentas where analysed for OPN and CEACAM1 expression. All placentas presented very strong expression of OPN in the extravillous (invasive) trophoblast (80% positive cells), which correlated with expression of CEACAM1. In addition, OPN was also present in the villous trophoblast, with strongest expression in the cytotrophoblast of the first trimester, while CEACAM1 was not expressed in the villous trophoblast. These data show that OPN is specifically expressed in the human placenta with strongest expression levels in the extravillous (invasive) trophoblast, where it correlates with expression of CEACAM1 and could thus contribute in the regulation of trophoblast invasion in a CEACAM1-involving mechanism as well as play an additional role in cytotrophoblast function.

(Supported in part by Deutsche Krebshilfe Grant No. 10–2063)