Stress neuropeptides in the human endometrium: paracrine effects on cell differentiation and apoptosis

Human endometrium exhibits characteristics of a neuroendocrine-like stress organ in addition to its classical role as the main target of ovarian steroid hormones. Indeed, the epithelial cells of human endometrium express the stress-associated neuropeptide genes corticotropin-releasing hormone (CRH), proopiomelanocortin, proenkephalin and prodynorphin. Furthermore, endometrium stroma cells also express CRH when they differentiate into decidual cells. Multiple lines of evidence suggest that the stress-associated neuropeptides of human endometrium are under the endocrine control of gonadal steroids as well as under an autocrine/paracrine regulation by prostanoids and interleukins. Endometrial stress-associated neuropeptides appear to exert their biological effect locally, i.e. within the uterus since human endometrium and myometrium also express the relevant receptors. More specifically, recent data suggest that endometrial CRH participates in the regulation of intrauterine inflammatory processes taking place in early pregnancy including stroma decidualization, blastocyst implantation and early maternal tolerance. Similarly, endometrial opioids participate in the regulation of uterine tissue remodeling via their effect on endometrial cell apoptosis. Thus, endometrial stress neuropeptides act as paracrine regulators of uterine cell differentiation and tissue remodeling as well as modulators of local immune responses.