Submitted January 28, 2003
Returned for revision February 22, 2003
Accepted June 5, 2003
Pregnancy
Induction of p38 Mitogen-Activated Protein Kinase-Mediated Apoptosis Is Involved in Outgrowth of Trophoblast Cells on Endometrial Epithelial Cells in a Model of Human Trophoblast-Endometrial Interactions
Hsin-Yang Li ,
Sheng-Ping Chang ,
Chiou-Chung Yuan ,
Hsiang-Tai Chao ,
Heung-Tat Ng ,
and
Yen-Jen Sung *
* To whom correspondence should be addressed. E-mail: yjsung{at}ym.edu.tw.
Abstract
During embryo implantation in species with hemochorial placentation, such as the mouse and human, trophoblast cells of the attached blastocyst penetrate the luminal epithelium of the endometrium before invasion into the endometrial stroma. Signs of apoptosis were demonstrated in luminal endometrial epithelial cells (EEC) adjacent to the trophoblast cells; however, the signaling mechanisms leading to apoptosis in EEC remain unclear. Since mitogen-activated protein kinases (MAPKs) were shown to mediate apoptosis in several model systems and found to be activated in the uterus during decidualization, the possible involvement of MAPKs during trophoblast-EEC interactions was studied. By co-culturing BeWo human trophoblast spheroids with RL95-2 human EEC monolayers to mimic the blastocyst-endometrial interaction, we found that most spheroids rapidly attached to EEC monolayers and then progressively expanded with marked dislodgment of EEC adjacent to the spreading trophoblast cells. Immunoblotting analysis showed that both p38 MAPK and extracellular signal-regulated kinase (ERK) were activated in EEC after co-culture. However, only SB203580 (a p38 MAPK inhibitor), but not PD98059 (an ERK inhibitor), inhibited trophoblast outgrowth on EEC monolayers through the suppression of p38 MAPK activation in EEC. Furthermore, trophoblast expansion caused prominent EEC apoptosis at the spheroid-EEC interface, as detected by annexin V labeling and valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (VAD-FMK, which binds activated caspases) staining, and SB203580 significantly decreased the percentage of apoptotic cells. Our results based on a model of human trophoblast-EEC interactions establish that trophoblast cells cause activation of p38 MAPK in EEC and, consequently, induce apoptosis and displacement of EEC, a process that may facilitate implantation.
Key words:
Apoptosis •
Implantation •
Signal transduction •
Trophoblast •
Uterus
