Implantation, Pregnancy and Parturition
(M586) THE INDUCTION OF OSTEOPONTIN IN OVINE ENDOMETRIAL STROMAL CELLS REQUIRES CONCEPTUS ATTACHMENT.
Burghardt, Robert1, White, Frankie1, Greggs, Schylr1, Spencer, Thomas 1, Johnson, Greg 1, 1 Texas A&M University, College Station, TX
ABSTRACT- Osteopontin (OPN), an integrin-binding extracellular matrix protein with cytokine properties, has been implicated as a contributor to implantation and conceptus development. Expression of OPN at the conceptus-maternal interface, beginning at peri-implantation and continuing throughout pregnancy, is regulated by steroid hormones in all mammalian species examined. However, comparative placentation studies suggest additional functions for OPN to regulate conceptus invasion through endometrial stroma, where the extent of OPN expression correlates positively with degree of conceptus invasiveness. In mice and primates, OPN is highly expressed in the decidua, whereas trophoblast invasion and stomal OPN expression does not occur during epitheliochorial placentation in pigs. Synepithelial implantation in sheep is more invasive than in pigs, involving erosion of the uterine luminal epithelium (LE) and fusion of trophectoderm with LE; and expression of OPN mRNA and protein along with other decidualization markers was observed in uterine stroma. Our objective was to determine the regulation of OPN in uterine stroma of sheep using unilaterally pregnant sheep in which one uterine horn was ligated and the ipsilateral ovary removed to allow comparison between non-gravid and gravid horns. OPN mRNA was detected in glandular epithelium (GE) of both gravid and non-gravid horns and immunoreactive OPN protein was present on LE in both horns. Significant amounts of the bioactive 45-kDa OPN fragment were secreted from the glandular epithelium and accumulated in the uterine milk of non-gravid horns. A high molecular weight form that likely represents multimeric OPN was present in allantoic fluid, but OPN was not detectable in amniotic fluid. Stromal expression of OPN mRNA and protein was markedly different between non-gravid and gravid horns with the gravid horn exhibiting extensive expression throughout the stroma whereas OPN mRNA and protein were barely detectible in the non-gravid horn. Pregnancy hormones were not sufficient to elicit OPN in the stroma of non-gravid horns, suggesting that stromal expression of OPN requires the immediate presence of embryonic tissue. We hypothesize that paracrine and/or physical effects from the conceptus induce changes in uterine stroma essential for placentation in sheep.
KEY WORDS: osteopontin, implantation, pregnancy, decidualization