Apoptosis in Human Amnion

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This study was designed to detect apoptosis in the human amnion and to elucidate its signalling. Samples of human amnion were obtained from 34 women (11th-42nd week of gestation) and studied usins the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labelling (TUNEL) method by light microscopy (LM) and transmission electron microscopy (TEM), immunohistochemistry, and caspase activitv assay. The TUNEL method by LM demonstrated that the percentage of TUNEL-positive cells in the amniotic epithelium was the highest in the 40th-41st week of gestation (P <0.05) independent of the onset of labour, and the cells were often detached from the epithelium into the amniotic cavity at term. The TUNEL method by TEM clearly showed the characteristic features of apoptosis such as the nuclear condensed chromatin with abundant free 3'-OH DNA ends, cell shrinkage and decrease in the number of desmosomes, except for the presence of apoptotic bodies. Fas and Fas ligand (FasL) were constantly expressed on apical membranes of amniotic epithelial cells through the 16th-27th to 40th-41st week of gestation, while no Bcl-2 expression was observed throughout the gestational periods. Activities of caspase-3 and -8, but not that of caspase-9, were higher in the 40th-41st week than those on the 16th-27th week of gestation (P <0.01). We conclude that apoptosis in term amniotic epithelium is independent of Bcl-2 regulation and onset of labour, and may play an important role in the fragility and rupture of human foetal membranes at term.