Activation of Delta-Notch signaling pathway promotes the development of the vascular system in embryo, normal adult tissues and cancerous lesions. Delta and Notch genes are known to be expressed in endothelial cells and little is known of their expression beyond the vascular system. The purpose of this study was to investigate whether Delta gene would be expressed in cells of the uterine endometrium.

In this study, we found that the human endometrial cells expressed one of the Delta ligands, Delta-like 4 protein (Dll4). Dll4 was expressed in human endometrium in a spatiotemporal fashion. Immunohistochemistry studies showed the cytoplasm as well as membrane staining with apical localization both in the luminal and glandular epithelium and moderate diffuse staining in the cytoplasm of the stromal cells. Western blot analysis showed that the size of the endometrial Dll4 was identical to that in the human umbilical endothelial cells.

The expression Dll4 mRNA in human endometrial cells was quantitatively determined by Real-time PCR. Dll4 mRNA expressed in the glandular epithelium showed large variations and it was significantly elevated in the mid and late proliferative and early secretory endometrium. Endometrial stromal cells contained less Dll4 mRNA and had no clear correlation with the menstrual cycle. The effect of hormones was studied in the primary culture of isolated glandular epithelial and stromal cells. In glandular cells, estradiol (E2) had little effect and medroxyprogesterone acetate (MPA) significantly reduced the mRNAs compared to that of control. Relaxin induced the Dll4 mRNA. In stromal cells, both E2 and MPA reduced the Dll4 mRNA.

To our knowledge, this is the first report of the expression of Dll4 in the endometrium. We propose that endometrial Dll4 may enhance the development of the endometrial microvascular system and facilitate the implantation of blastocyst in a fertile cycle.