Co-existence of heparin-binding epidermal growth factor-like growth factor and pinopodes in human endometrium at the time of implantation

Pinopodes have been suggested to be markers of uterine receptivity. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is expressed in increasing amounts in the secretory phase endometrium and is considered to be important for the human implantation process. The aim of this study was to investigate a possible co-existence of pinopodes and HB-EGF in the normal human endometrium. Endometrial biopsies were obtained from women with normal menstrual cycles. The biopsies were examined by scanning electron microscopy for the detection of pinopodes, by immunohistochemistry for the expression of HB-EGF protein, and by confocal microscopy to determine if HB-EGF was present on the surface of the pinopodes. The expression of HB-EGF in luminal and glandular epithelium was highest when fully developed pinopodes were present. Using confocal microscopy it was shown that HB-EGF was present both inside the luminal epithelial cells and on the surface of pinopodes. These findings suggest that HB-EGF might play a role in both the attachment and penetration steps in the human implantation process. Furthermore, the immunohistochemical staining demonstrates that HB-EGF can be used as a marker for the implantation window.