Expression of uteroglobin in the human endometrium

Uteroglobin is a progesterone binding protein, a member of the antiflammin gene family and possibly a novel cytokine. Initially, uteroglobin was ident ified as the major protein of rabbit uterine secretion during the phase of preimplantation. Counterparts of the rabbit uteroglobin or its gene are des cribed in rat, mouse, hamster, hare, pig, horse and human. While uteroglobi n appears as one of the most extensively studied proteins, particularly its physico-chemical properties, including its crystal structure and its gene, the true physiological role of this protein still remains to be unravelled . Essential to understanding the significance of human uteroglobin in repro ductive organs, particularly in the endometrium, is a knowledge of the spat ial and chronological expression of this secretory protein. Our studies on 115 volunteers combined reverse transcription-polymerase chain reaction (RT -PCR), immunohistochemistry and quantitative assessment by an enzyme-linked immunosorbent assay for uteroglobin. The expression, localization and rele ase of uteroglobulin in the human endometrium are presented. Secretory uter oglobin is found in endometrial tissue homogenates in highest levels of exp ression during the early luteal phase (days 15-19, 340 pg/mg total protein) . In turn, uteroglobin is released into the uterine lumen in peak amounts d uring the receptive phase of the menstrual cycle (mid-luteal phase, days 20 -23, secretion level 833.4 pg/mg total protein). Our immunohistochemical st udies match with these results, as uteroglobin is located during the early and mid-luteal phase in the apical compartments of endometrial gland cells. These observations strongly suggest an involvement of uteroglobin in endom etrial preparations for implantation.