Abstract: 307

CHARACTERIZATION OF APOPTOTIC DNA FRAGMENTATION, FAS AND FAS LIGAND EXPRESSION IN THE HUMAN PLACENTA.

Qing Qiu¹ , Andree Gruslin¹ , Benjamin K. Tsang^{1 *}
Division of Fetal-Maternal Medicine and Reproductive Biology unit, Department of Obstetrics Gynecology and Cellular Molecular Medicine, University of Ottawa, Loeb Health Research Institute, Ottawa, Ontario, Canada K1Y 4E9 ¹

Although apoptosis in the human placenta occurs throughout gestation, the specific cell type(s) involved and its association with the Fas/Fas Ligand (FasL) death pathway remain to be fully elucidated. The object of this study was to compare placenta apoptosis at different stages of pregnancy, identify cell types involved and relate these observations with changes in Fas and FasL expression. Placentas were collected from healthy patients in 1st, 2nd and 3rd trimester. Apoptotic cells were identified histochemically by TdT-mediated dUTP nick end-labeling (TUNEL) and quantitated on the basis of low molecular weight DNA fragmentation. Fas and FasL were localized by immunohistochemistry. The human placenta exhibited biphasic apoptotic DNA fragmentation response throughout pregnancy; decreased significantly from 1st to 2nd trimester and returned to high level near term. Apoptotic cytotrophoblasts (CT) which exhibited intense immunoreactivity for Fas but not FasL were most evident during the 1st trimester. While also present in the cytoplasm of CT, intense Fas signal was observed on the plasma membrane. In contrast, although FasL immunoactivity was high throughout the gestation, syncytiotrophoblast Fas immunostaining and TUNEL positivity increased during placental development. Extensive apoptosis and significant Fas expression were observed in the stromal cells during 1st trimester. These responses decreased during the next trimester but were markedly enhanced at term, particularly in cells in the perivascular region. Stromal cell FasL was only detectable during the 3rd trimester. These findings support our hypothesis that placental apoptosis, an important component of cell homeostasis during development, involves cell type-specific, cytodifferentiation-dependent Fas expression and paracrine FasL-Fas interaction. (Supported by the PSI Foundation).

    This abstract is being presented on Monday, August 2 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.