The glucocorticoid receptor is specifically expressed in the stromal compartment of the human endometrium

The human endometrium is a classical target tissue for steroid hormones. While the expression pattern and functional roles of both the estrogen receptor (ER) and the progesterone receptor (PR) are well defined, expression of the glucocorticoid receptor (GR) in this tissue has not been described so far. In the present study, we used immunohistochemistry to analyze the expression of GR in the normal human endometrium throughout the menstrual cycle. The expression of GR was compared to that of ER and PR, which were analyzed in parallel. We show that GR is expressed in the human endometrium with a pattern that markedly differs from the expression patterns of ER and PR. ER and PR are expressed in the nuclei of endometrial glands, whereas GR is completely absent from these structures. However, GR is strongly expressed in the stromal compartment of the endometrium throughout the cycle. Both stromal fibroblasts and lymphocytes are GR-positive. In addition GR expression is also observed in the endothelium of small endometrial blood vessels, which are ER- and PR-negative. Western blot analysis performed on endometrial tumor cell lines of glandular (HEC-1B) and mesodermal (SKUT-1B) origin, respectively, showed GR expression only in the latter. In summary, we demonstrate that GR is expressed in fibroblasts, lymphocytes and endothelial cells of the human endometrial stroma, while it is absent from the glandular compartment. The specific expression pattern of GR within the human endometrium points to a possible functional role of glucocorticoids in the process of decidualization which occurs primarily in the stromal compartment.