Expression of aminopeptidase N in human endometrium and regulation of its activity by estrogen

Objective: To determine whether aminopeptidase N (APN) regulates the cycle- dependent bioavailability of interleukin-8 (IL-8) in the endometrium. Design: Prospective study. Setting: University medical center. Patient(s): Women without endometrial pathology from the proliferative (n = 25) or secretory (n = 18) phase of the menstrual cycle. Intervention(s): We first immunolocalized APN in the endometrium using an a nti-APN antibody. We then determined the regulation of APN kinetic activity by sex steroids in endometrial stromal cell cultures. Main Outcome Measure(s): Expression of APN in human endometrium throughout the menstrual cycle. Regulation of APN activity by estradiol and progestero ne in cultured endometrial stromal cells. Result(s): Immunohistochemistry of endometrial sections revealed staining o f endometrial stroma throughout the menstrual cycle. There was no detectabl e staining in glandular cells. The expression of APN as detected by immunoh istochemistry was significantly lower in the early proliferative phase. In cultured cells, estradiol inhibited APN activity in a concentration-depende nt manner. Progesterone did not have a significant effect. Conclusion(s): Stromal localization of APN in endometrium may explain the e pithelial rather than stromal presence of IL-8 in vivo. Decreased expressio n of APN may increase IL-8 bioavailability thus contributing to angiogenesi s and polymorphonuclear leukocyte chemotaxis in early proliferative phase. (Fertil Steril(R) 2001; 75:1172-6. (C) 2001 by American Society for Reprodu ctive Medicine.).