Epithelial cell protein milk fat globule-epidermal growth factor 8 and human chorionic gonadotropin regulate stromal cell apoptosis in the human endometrium

Abstract

To study the regulation of apoptosis in human endometrial cells. The specific aims were to determine whether milk fat globule-epidermal growth factor 8 (MFG-E8), a novel endometrial epithelial protein, modulates caspase activation and DNA fragmentation; and to examine whether hCG, an early embryonic product, regulates Bax and Bcl-2 equilibrium, as well as MFG-E8 expression. Design: Primary cultures of human endometrial epithelial cells (EECs) and endometrial stromal cells (ESCs). Setting: Academic center. Patient(s): Ovulatory women aged 21-30 years. Intervention(s): Treatment with MFG-E8 and hCG. Main Outcome Measure(s): Apoptotic activity was quantified using a luciferase assay. Deoxyribonucleic acid fragmentation was detected by TUNEL assay. Bax, Bcl-2, and MFG-E8 messenger RNA expression levels were determined by quantitative reverse transcription-polymerase chain reaction. Immunocytochemistry was used to establish cell purity and presence of MFG-E8 and hCG-R (receptor) proteins. Result(s): Endometrial epithelial cells were cytokeratin+, vimentin-, MFG-E8+, and hCG-R+, whereas ESC were vimentin+, cytokeratin -, MFG-E8-, and hCG-R+. Treatment of ESC with MFG-E8 resulted in a 13-fold increase in caspase activity and a 30-fold increase in TUNEL. On the other hand, hCG decreased messenger RNA expression of Bax in ESC. Conclusion(s): Milk fat globule-epidermal growth factor 8 has proapoptotic activity, suggesting participation in endometrial remodeling via an epithelial-stromal cell paracrine effect. Conversely, pregnancy levels of hCG has opposite effects on stromal cells.