Apoptosis in human endometrium: apoptotic detection methods and signaling.

It is generally accepted that apoptosis occurs in human endometrium through the late secretory to menstruating phases. We found that Bcl-2 expression showed a cyclic pattern, peaking during the late proliferative phase. The decreased Bcl-2 in human endometrial glandular cells during the secretory phase was consistent with the appearance of apoptotic cells during the same phase. The expression patterns of both Sp-3 and c-Jun in glandular cells were similar to that observed in Bcl-2. Therefore, Sp-3 and c-Jun could be candidates for bcl-2 transcriptional factors in the human endometrium. In contrast to Bcl-2, both Fas and Fas ligand in glandular cells were coexpressed throughout the menstrual cycle. In particular, glandular cells showed the most intense expression of Fas ligand from the secretory to menstruating phases. The activities of caspase-3, -8 and -9 were higher from the secretory to menstruating phases than during the proliferating phase. We therefore conclude that bcl-2 transcription in glandular cells may be promoted by the binding of several transcriptional molecules to bcl-2 promoter, and the translated Bcl-2 blocks the release of cytochrome c from mitochondria to the cytosol during the proliferative phase. During the secretory phase, glandular cells may undergo apoptotsis via both death-receptor and mitochondrial pathways.