Menstrual-like breakdown and apoptosis in human endometrial explants

BACKGROUND: Apoptosis occurs in late secretory and menstrual human endometrium and is thought to play an important role in endometrial physiology. Menstrual-like breakdown has been observed in vitro in endometrial explants. The purpose of this study was to assess the role of apoptosis in menstrual-like breakdown in human endometrial explants. METHODS: Human endometrial tissue was obtained during the mid-secretory phase and cultured with or without estrogen and progesterone. The occurrence of breakdown was assessed by histology. Apoptosis was determined by gel electrophoresis for the detection of DNA fragmentation and by immunohistochemistry using the M30 CytoDEATH and anti-cleaved caspase-3 (CASP3) antibodies for the detection of caspase activity. Expression of BCL2 and BAX was quantified using real-time PCR analysis. RESULTS: Apoptosis occurred in human endometrial explants at all time-points studied. Cleaved CASP3 and M30 antigen expression increased in all explants, suggesting the involvement of CASP3 in the apoptosis. Low BCL2:BAX ratios were observed in all samples when compared with pre-culture controls. Estradiol and progesterone supplementation of the culture media reduced or eliminated menstrual-like breakdown but did not affect the degree of apoptosis observed. CONCLUSIONS: The apoptosis observed in endometrium during the late secretory phase and menstrual phase does not appear to be mechanistically related to the tissue breakdown but rather may be involved in the impending remodelling that occurs in the endometrium in the transition from secretory to proliferative phase following the menses.